To see who last visited your profile, just select "Profile visitors" on your homepage. Alternatively, select "Matches" in the top bar and then select "Visitors".
If you're on a mobile device, you will be able to find "Visitors" in the menu next to your number of matches.
"NEW" will appear on the profiles of those matches that you have not yet viewed. If the profile does not have "New" on it, this mean s that you have visited this profile.