Help: Select whether you want to search for a Forename, a Surname etc. from the drop-down list. Then specify the actual text to search for in the next box, and (optionally) enter the year the person left Longlands.
A '*' character in either text box means 'match anything'. So, for example, 'jo*' would match 'Jones', 'Johnson' and 'Jovanovich' (assuming you chose to search for surnames), and '197*' would find matches from the whole of the 1970s.
If you specify a starting or leaving year (or a decade such as 198*), this will exclude all users who have not entered a starting / leaving year in their profile.