Hi Michelle,

The documentation will vary slightly from brand to brand, but you should be walked through everything in detail and don't hesitate to ask questions if you're unsure of anything. 

In general, there will be a sales contract to sign in various places, usually detailing the transaction in terms of how much is being offered for your trade-in and the final price to be paid etc. The dealer will take care of the change of ownership of your trade-in. 

Of course, if you're taking out finance, then that will require separate paperwork.