As long as you meet the entry requirements for a raffle, entering is as simple as clicking on the Register button. If you do not meet a requirement, the requirement will be highlighted in red along with a cross icon on the left of it:
If you have currently entered, or previously won a raffle for a specific project with your selected wallet, but you select that same wallet to enter a raffle for the same project, then an amber warning as shown below will appear. This is only a warning to inform you and can be ignored if you prefer to continue with the same wallet.
As with all warnings and errors, more information is shown upon hover.