Grolam: You are right, mutagens are potions made from special ingredients from bosses. Some mutagens grant you a specific talent. If you consume such a mutagen, you receive the respective talent. I think there is obvious notification which talent you just received.
However, not all mutagens give you specific talents. Some give you additional talent points you can spend just like points gained by gaining a level.
Either the mutagens you consumed gave you talent points or you did not notice that you had acquired a new talent.

bigpap: Is it one time occurence or do I have to drink a potion everytime I want to gain this mutagenic ability?

Waltorious: I don't remember exactly, but I think drinking the potion will automatically give you the ability; you don't need to also spend a talent point. Also, it's a one-time thing, and you will keep the ability forever.

These types of mutagen potions are basically rewarding Geralt for beating the boss by granting him a special new skill. But instead of just learning it automatically, he does it with a mutagen potion because that fits better with the Witcher lore.

bigpap: While I'm at it, what does 'requires student' mean?

bigpap: Thanks for the reply, seems like I misunderstood. mutagenic potions apparenlty aren't the same as mutagens. The latter is an ingredient much like vitriol, rubedo, etc. Drinking mutagenic potions does give me +1 talent point but doesn't let me select abilities that have the words 'requires consumption of mutagen' in place of 'requires bronze talent''.