Things to Do in Auschwitz
Unlike other tours and visits in Poland, this one is not the most pleasant, but it will certainly leave a lasting impression on you. Auschwitz is a must-see, so I'll tell you what you'll see there.

Detail of Auschwitz concentration camp | Frederick Wallace
If you are organising a visit to the famous Auschwitz concentration camp, you should know that there are mainly two ways to visit it: either on your own, by buying tickets to Auschwitz or by joining one of the Auschwitz tours from Krakow.
I personally recommend the second option: besides not having to worry about the logistics of getting there, you will be accompanied by an expert guide who will help you understand this tragic episode in history and contextualise the rooms and different parts of the extermination camp.
In any case, throughout your visit to Auschwitz, you will see the two main camps that form part of the larger Auschwitz Birkenau complex: Auschwitz I and Auschwitz II (the two are only 3 km apart). Here is a list of what you will see during the tour.
Auschwitz Camp I

This is the entrance to the extermination camp and the original part of the Auschwitz-Birkenau complex. It was built in 1940 by the Nazis with the idea of holding between 15,000 and 20,000 prisoners. The tour of Auschwitz begins here, where the visitor centre is located.
You will immediately recognise the iron gate that appears in all the photos, headed by the famous writing "Work will set you free".
The visitor centre's short documentary

Before starting the tour, the visitor centre offers a short documentary film (about 15 minutes) to help you contextualise what you will see next.
In my opinion, it is worth the time (especially if you have not hired a guide or audio guide for the visit) because it is very dynamic and everything is very well explained. The documentary is in black and white and shows original images from the period.
The large barracks with artefacts and photos of the victims

The first thing that will strike you when you enter the area will be the huge brick barracks where the Jews arrived and where they were housed during their stay in the camp.
Some of them have now been converted into a museum, where some of the prisoners' belongings that were recovered after the liberation of the camp are on display. You will see small objects of personal hygiene, clothes, shoes, suitcases... At this point, the tension of the visit starts to rise and become more intense.
The exhibits inside the barracks
Along some of the corridors you will also see endless walls filled with pictures of the Jews whose lives ended in Auschwitz. On them, you will see the date of their arrival at the camp and their date of extermination. While those who arrived during the first few months spent a long time working there until they were exterminated, those who arrived last barely lasted weeks or months before their lives ended.
If you go with children, my advice is not to linger too long in this part of the exhibition, as the details may offend their sensibilities (there is even a large room with the hair that was shaved off the prisoners on arrival).
The old railway tracks

Along one side of the camp and also linking the first and the second, you will see abandoned railway tracks. These tracks were used to transport prisoners from one camp to another or to receive them from different parts of the country and the rest of Europe.
The guide will give you an insight into how these transfers were carried out and how the prisoners were crammed into crowded wagons. Today these train tracks are no longer used for anything, but are maintained as part of the Auschwitz memorial.
Auschwitz II - The Great Auschwitz II Open Grounds

After an emotionally charged visit to Auschwitz I, it is time to move on to Auschwitz II. This part is much less touristy and less visited than Auschwitz I, but also, being so large and with so few barracks still standing, it gives you a much greater sense of coldness and abandonment.
This camp was built by the Nazis as an extension of the first camp. The number of Jews that could be held here was much greater: up to 90,000 prisoners were held here simultaneously.
The speed with which this part of the camp had to be built meant that the materials used and the quality of the barracks was much worse: wood was used and the spaces were completely open-plan so that as many people as possible could fit in. Shocking. Very few are left standing.
The gas chambers

Some of the gas chambers used in the extermination of prisoners in this camp have been preserved and you will be able to visit some of them. The guide will explain how the Nazis who ran the camp tried to blow them up when the liberation of the Jews began. They tried by all means to eliminate the tortures to which they subjected their prisoners. Today they are preserved as they were after that.
The walk through this area is, needless to say, a truly grim experience. If you also visit Auschwitz in winter, you will see that the temperatures, the humidity and the feeling of cold in the middle of this wasteland is terrible. Imagine what it was like for the prisoners there, dressed in simple cloth pyjamas and practically without food for days, weeks or months.
While initially it seemed that these camps were meant to be labour camps, with the short passage of time they turned directly into extermination camps. Wagonloads of people arrived who never even made it to Auschwitz, but instead "landed" en masse in these gas chambers where their lives were ended.
The watchtower

One of the highlights of this part of the camp is the watchtower, which is still standing and which you can climb for a panoramic view that will help you understand the enormous dimensions of Auschwitz-Birkenau. The view from the top is bleak, especially if you try to imagine what the real views of the Nazis guarding the prisoners were like from here. Terrifying.
The barbed wire surrounding the camp

Another thing that surprised me was to see that the miles of barbed wire surrounding the camp, which perimetered the little space of freedom and movement that the prisoners had, are still standing. If you have time after your visit to walk around the camp, you will see that some of the huge houses that were once the homes of the Nazis who ran the concentration camps still remain.
A terrible contrast to the living, working and torture conditions to which the prisoners were subjected for years in this place.
Auschwitz Prisoners' Life in Auschwitz

One of the things that struck me most during the tour, apart from the details and objects that you will see during your visit, was that only when you are there do you get an idea of the daily life of the prisoners.
Until then, I had heard and read about many episodes from this part of history, but when I got there, saw the dimensions of the camps and heard from an expert guide what the prisoners' daily lives were like, I really got to imagine how all the people who passed through there lived.
If you take the guided tour, they will explain to you what the schedules, routines and functioning of the different pavilions were like, always with respect for the memory of the victims. It is definitely a reality check that you should get to know so as not to forget one of the worst episodes in the most recent history of humanity.