Hi,
This should be quite easy.
First you need to select the track you wish in your library using the tree, the panes or the search dialog. Then as the selected track is highlighted :
Right Mouse Click / Play will onlly play your selected track.
Now if you want to have the same effect with the main Play button you need to go to Option/General/Play Button and choose 'Play visible files (selected)' in order to only send the selected track to the 'playing now' playlist.
Another way is to use the search dialog to select your track and then the combination <Shift><Enter> will only play the track found.
i.e. : If I only enter the keywords 'Stones Jumpin' the selection will find one track : 'Rolling Stones - Jumpin' Jack Flash' that I can play instantly using <Shift><Enter> (Keywords to enter depends of the richness of your library)
Hope this helps,
Have a great sunday,
C.