Over the course of a game, your character will do many things. Some of these tasks are considered actions, while others aren't. Speeches and conversations aren't considered actions as such - but just about everything else, from throwing a punch at your sire to trying to decipher a code, is probably an action. One action typically takes one turn (see above) of game time to complete.
It's easy enough to attempt an action - just tell the Storyteller what your character's trying to do and how she plans to go about it. And most actions - crossing the street or loading a pistol, for instance - are easy enough to be considered automatically successful. However, if you're trying to cross a four-lane highway full of speeding trucks, or trying to reload while you're hanging from a fire escape by one hand, there's a chance you might fail. So when there's reasonable doubt whether an action will succeed or not, you may have to roll dice to determine the results.
Not everything that your character actually does counts as an action. For instance, spending a blood point to increase an Attribute is considered to take less than a second of game time - no dice are rolled, and your character can do this while doing something else. Such a "free action" is called a reflexive - in essence, a feat that doesn't require taking an action to accomplish.
Reflexives include such activities as spending blood points to increase Attributes, soaking damage, making a Virtue check, or activating Celerity to take extra actions. They aren't considered actions in any real way - you don't have to subtract from your dice pool to soak damage while you're firing a gun, for example. Of course, you still have to be conscious to perform many reflexives, but they don't get in the way of anything else you want to do in a turn.
