Where and how to verify third party vst-plugins and sound files .wav etc. after install and path scan in settings.
Which exact version and variant (Free, Plus or Premium) of MM do you have?
Assuming you have either the Plus variant (and have elected to add the additional features to allow use of VSTs, or the Premium variant, which includes the facility to use VSTs) the .dll files which every VST or VSTi uses can be seen and used in MM provided that you have specified the directory/directories in which they are located. You tell MM where to find your VSTs and VSTis via Program Settings>Folders>Add VST plug-in path.
You should not need to verify ... sound files .wav etc. since simply importing one or more to a track or tracks should enable them to be played back and used.
If this does not answer your questions, please give us a lot more detail about what are the exact problems you are experiencing.
HTH
Jeff
Forum Moderator