Yes, we actually encourage all users to perform several mock/practice drafts before their actual draft.
This will assure that everything is setup and running smoothly, as well as allowing you to become with the interface and all of the tools and features that are available.
To do a mock/practice draft, simply select DRAFT > START A NEW DRAFT, and start performing a draft.
If you want to start over, just select "DRAFT > START A NEW DRAFT" and it will overwrite all of the previous info from the prior draft, and so you can start from afresh.
When performing Mock / Practice Drafts, if you utilize the "Team on the Fly" or "In-Draft Trades", this can alter the draft order picks permanently. It is very important to make sure to change this back by going to SETUP > DRAFT ORDER SETUP, and double-checking your "Individual Draft Order Picks" prior to the actual draft, and resetting back any changes that were made during Mock Drafts.