Simply select the heart icon to add someone as a favourite.
In search results, you'll find it next to the envelope icon.
You are most probably making your search criteria too narrow. Matches are other members whose profiles meet the criteria you specified in your My Ideal Match page when you set up your profile.
You can view other people's profiles by searching the site and, in turn, they can view your profile.
When you find someone that interests you, you can send a message via the site to their username.
Knowing when someone last logged in is very useful when you look at their profile.
If you're on a mobile or table device, click on the info icon ('i') next to the favourite icon in search results or to the right of the match % when viewing a profile.
Make sure your profile is as complete as possible and that your desired partner details are not too open.