“I'll be there bright and early!”
You've got a new job that you're starting tomorrow. Your new boss has called you to confirm that you're starting tomorrow. You want to sound enthusiastic, so you say this.
I'll be there bright and early!
To "be there" means to attend. You can say:
I'll be there.
You can also say when you're going to arrive:
I'll be there at eleven.
This is a very natural and casual way to say that you're going to come to an event, meeting, or party. You wouldn't use this in writing, but it's common in business communication.
"Bright and early" means "early in the morning". You use it to talk about waking up early, starting work early, exercising early in the morning, and so on:
We're going to get started bright and early tomorrow!
"Bright and early" sounds energetic and positive.