The Star Wars Roleplaying Game uses a core mechanic to resolve all actions. This central game rule keeps play fast and intuitive. Whenever you want to attept an action that has some chance of failure, you roll a twenty-sided die (or ?d20?). To determine whether your character succeds at a task (such as a attack, the use of a skill or ability, or an attempt to save your character from harm), you do this:

Roll a d20.
Add any relevant modifiers.
Compare the result to a target number.

If the result equals or exceeds the target number (set by the GM or given in the rules). Your character succeds at the task at hand. If the result is lower than the target number, you fail.