When you're really anxious and jumpy, you can say you have the jitters. Your jitters might make it hard to stand calmly in front of an audience and deliver a speech.
Jitters is an informal but useful noun that captures the fidgety, nervous feeling that everyone gets sometimes. When you have the jitters, you're so nervous you can hardly sit still. This word is one of the relatively few coined in the United States, and it's thought to be influenced by chitter, in dialect "tremble or shiver," from Middle English chittern, "to twitter or chatter."