In Aftermath the acquisition of skills is not a representation of learning skills per se, but rather remembering the skills your character used to have. At the start of the game your character has forgotten all but their most basic of skills. Over the course of the game, your character slowly regains some of their memories in the form of skills they used to know. In the first term they shall be able to remember some of their more specialized skills and in the second term they will start to be able to remember even the most complicated of their previous abilities. It is worth noting that your character is not making an in-character decision to remember a specific skill, but it is your own out-of-character decision as to which one they do relearn.
In Aftermath, there will be automatic character advancement. Every other turn (starting with turn 1) your character will be able to remember a skill. You may choose to relearn any skill that is available to you.
Due to the patchy nature of memory restoration, none of the skills you remember will require you to have previously remembered any particular skill. It is possible for a character to only remember the most advanced specialisation of a discipline. Your character before the events of Aftermath may have known all of the more fundamental aspects of that discipline, but only the advanced skill has come back to them. For example it may be possible to remember the commanding skill, without having the basic organization to gather a group of followers to start with.
The process of remembering a skill is a slow one and therefore skills remembered may not be used in the same turnsheet that they are acquired in.
In Aftermath, gaining skills through teaching or tutoring will not be possible.