First you'll probably have to install them on your computer, then all you will need to do is get the files specified on the scummvm site from the installation and copy them to the appropriate directory to set it up.
Say you have Day of the Tentacle cd/disks, install the game, then look for the files TENTACLE.001 TENTACLE.002 MONSTER.SOU (and if you want to play Maniac Mansion in DotT copy the "maniac" directory too).
Set up ScummVM to use those files wherever you put them and your good to go.