As an example, here are the search results for Beethoven violin sonatas. (This was an Advanced Search in which Beethoven's name was typed into the first search box, as the author, and "violin sonata" was typed into the second search box, as keywords.)
Most search results will say the location of each score is Main Library 4th Floor - Books
Go to the fourth floor and find the shelves with the call number "M"
Search for the specific call number of the score you want [like M219.B4 S6 D6, 1990]
Take your score to the main lobby's help desk and check it out
Note: Some scores are in a closed collection. If, in your list of search results, your score's location says Main Library Storage, then choose Access options - Request it. The library staff will get your score, send you an email letting you know it's available, then you can pick it up at the help desk
If you would like to look at all of the fourth-floor scores for a specific genre or instrumentation (solo guitar music, string quartets, symphonies, piano concertos, etc.), first consult the call number guides listed below
Music Scores: Instrumental, Solo & Small Ensembles