Vassal modules are not “computer games” per-se, but a computer based implementation of the board and counters.
Thus, you have to do the same kinds of things you have to do in a Face-To-Face game. Move the counters, declare your attacks, etc. It’s up to you and your opponent to make sure you follow the rules - the module does not enforce them.
So for instance - move a group forward, rotate it to face what you are attacking, announce (verbal chat or type) the attack type/strength, roll the dice, implement the results, etc.
By the way - please not post questions in NEWS posts, these are for public service announcements and the like…