The sentencing range for first degree robbery is 3, 6 or 9 years in state prison; for second degree it's 2, 3 or 5 years in state prison. If this is your first offense probation may be possible with a hefty county jail sentence. Robbery is also a strike which will have consequences on the amount of time you actually serve as well as possible future offenses.
Mr. Kaman has covered the basic sentence ranges for robbery charges. There can be enhancements for the use of a weapon (particularly a firearm), the age of the victim, whether or not injury was inflicted and how what the value of the property taken was.
Robbery, as a strike, carries a presumption that if convicted, you'll be sent to state prison. That's a presumption only and with no prior record, a probationary sentence and county jail time are distinct possibilities.
Make sure you know that you don't have to prove your innocence - it's up to the DA to prove you guilty beyond a reasonable doubt. If they can't, you walk.
Given what's at stake, you need to find the very best criminal defense attorney you can find to help you.