If you find a member particularly interesting, visit their profile and click/tap Add to Favourites.
They will be marked with a star and can be found under Matches by applying the filter Favourites.
To remove a match from your Favourites list, simply visit the profile and click/tap Remove from Favourites.
On the iOS app, add or remove someone from your favourites by visiting the profile and tapping the small heart in the top right-hand corner of the profile.
Likes and Favourites are currently not available on the Android app.