Actions, as in the number on a Character Card is simply the number of actions a character gets to use in a turn.
Actions are a type of ability.
Other ability types are Health abilities, Ongoin abilities, innate abilities (which will also be ongoing, or actions, etc.) and Omni-cannon which triggers using tokens.
When you use an action you aren't consuming an action, you are using up one of the actions you get that turn.
Tachyon gets 3 actions each turn, if she uses an action, she only has 2 actions left. Which is just easier than saying:
Tachyon may use 3 action abilities each turn, when she uses an action ability it will count toward her limit of three action abilities per turn, reducing the number of action abilities she can still use this turn by 1, leaving her with the option of using up to 2 more action abilities this turn, before she will have reached her limit and thus will be unable to use any more action abilities this turn.
The second is what is actually going on, we just shorten the explanation.