Kaer Morhen - main quest
Important - before starting the proper game, you must choose difficulty level and decide whether you want to see hints. Additionally, you must decide whether you want your decisions to be transferred from the second installment of the series. If you have a PC version of the game and saves from Witcher 2, you can upload them. If you don't have saves or if you're playing console version, then you can decide whether you want to determine most important decisions (it will be done after reaching a palace later in the game) or does the game should make those decisions for you. More information about importing decisions from previous game can be found in a different chapter of this guide (transferring decisions from Witcher 2).
Prologue of Witcher 3 takes place in Kaer Morhen fortress. It is a tutorial that allows you to learn the basics of the game. You start in Yennefer's bedroom. Use Witcher Senses to find a key to the bedroom door - it is lying on one of tables, on an open book. Walk down to the lower floor of the fortress to meet Vesemir and Ciri. You can agree to participate in a race to the lower courtyard or refuse. If you choose the first option, then you will learn the basics of moving - sprint, climbing, jumping over obstacles and jumping down.
On the lower courtyard Vesemir will ask if you want to participate in a sparring. You can tell him to remind you the basics or immediately start the training. If you picked the first option you will learn all of the most important fighting techniques - choosing the right sword, marking targets, fast attack, strong attack, dodging, counterattacking, using signs, throwing bombs. Soon the prologue will end.