I thought I'd add an updated guide on how to get to Auschwitz by bus, as it was a little confusing when my mom and I went. I hope it makes sense and helps you all :)
1) Go to the bus station (Dworzec Autobusowy), which can be accessed via Krakow Glowny Rail Station; you can either walk to the bus station itself (to the right of the train station, if Krakow city is to your left), or you can enter through the 'Galeria Krakowska'.
2) If you enter through the Galeria (which takes you to the train station), make sure to go down any escalator and down to the level that is beneath the rail lines. There should be signs directing you to the bus station - the two are next door to each other.
3) When you enter into the bus station (you will go up a tiny flight of stairs to enter into the station), on the right hand side you'll see a massive board with RED, WHITE, YELLOW, and GREEN-coloured words on it. Look for the name 'OSWIECIM'. Here it will list times at which the bus leaves. It is confusing to read and work out :)
4) Go down a level (there is a lift, and a set of stairs in the very middle of the bus station so you can't miss it). Head to stand D8 (this was the stand we went to to get the 07:10 bus).
5) You can buy your ticket on the minibus (which is what the ticket seller lady upstairs told me) for 12 zloty for a ONE-WAY.
6) Be sure to get to the bus quickly, because it does fill up. Along the way the bus will fill up with more people, and can become a bit stuffy and uncomfortable.
7) The driver will know that a lot of his passengers are going to the camp, so he will make the stop outside Auschwitz. Upon arrival at the camp, he will give you a timetable of return times on his minibus.
8) The minibus stops at the back of the camp and it's easy to find your way to the Auschwitz entrance. Where this bus dropped you off, it will pick you up from again.
---GOING FROM AUSCHWITZ 1 TO AUSCHWITZ BIRKENAU---
1) Find your way to the parking lot of Auschwitz 1. Here you will see parked many many buses.
2) Find the 'SNACK BAR'.
3) On the very same road, and to the right of the SNACK BAR you will see a pole with bus times on it. This is where the FREE bus shuttle stops to take passengers to Birkenau.
PS: DO NOT get confused here, because the BIRKENAU bus shuttle times are posted on the opposite side of the SNACK BAR. The bus time mentioned in #3 just above are the times the bus to KRAKOW leaves, however this is where the SHUTTLE bus picks you up from.
4) The bus is black, and says on the top of the window 'BIRKENAU'. This bus will take you to the Birkenau camp.
5) Where this bus drops you off, it will pick you up from again. It is very near to the 'Gate of Death'.
- If you decide not to take the mini bus back to Krakow, you can take a bus which stops (at Auschwitz 1) at the same place where the BLACK SHUTTLE BUS picks Birkenau visitors up from.
- If you know for certain that you'll be using the minibus again (which brought you from Krakow), you can buy a return ticket from the bus driver in Krakow. Otherwise I'd imagine that you can just buy the return ticket on the minibus at the back of Auschwitz 1.
I really hope this helps. And if you have any questions, I will try my best answer :)