You gain a skill point every time you gain a level which can then instantly be invested into a Skill. All the current Skills have a maximum rank of 10 and a minimum rank of 1 meaning that you must invest at least 1 point in a skill to be able to use it and at level 10, the skill will be maxed and you can't invest any more points into it.
All the skills have a Turn Cost, Duration and Cooldown time. It costs a certain amount of turns to cast a skill and once you cast it, you have until the Length timer runs out to make use of it. The Recharge timer will then show how long it will be until you can cast the Skill and reap the benefits again!
Additionally, some skills will have either a minimum level requirement or a targeting ability, or both! The minimum level is to stop lower levelled players having access to overly powerful skills early on and the targeting ability allows you to cast skills on other players, either to help or hinder them.
It has been announced that new skills may soon be available which is welcome news as many of the higher level players will have skill points building up that they are waiting to spend. Feel free to suggest new skills on the Forums!
As for which Skills to use on your character, It often comes down to trial and error and deciding what you like and what you think you can make use of. There is an option to reset and re-allocate the points that you invest in your Skills if you decide you’ve made a bad decision. This is found in the Upgrade Centre and has a point cost.