Some websites will ask you to fill out a registration form before you can use them. While this is normal, it's a good idea to find out what the website will do with your personal details.
All companies that collect information have to tell their customers how personal information will be used. Make sure you check the website's terms and conditions if you want to know.
Some sites allow other companies to use details from their user database for market research purposes. Companies have to give you the chance to tell them if you don't want your details to be used in this way. This is often done by having a tick box on the online registration page. If you don't want your information to be used, tick that box before you submit your information