It’s your profile, so you’re in charge. To block a member just go to their profile and select ‘Block’. This will stop them from viewing your profile, contacting you, or seeing any of your activity.
If you later want to unblock someone, just go to your Preferences and here you will find your list of blocked users under Advanced settings.
If you’re blocking someone because they’ve behaved inappropriately, please also report them to us so we can look into it and help keep our community safe. You can find out how to report someone here.