On the site, users can find a variety of musical scores, parts, solos, and audio recordings. It should be noted that the IMSLP database is primarily represented by music of the Western tradition, and those in search of works from outside this realm will have significantly fewer options. Scores by European composers from the 18th and 19th centuries are the most common, while works by those from early 20th century slowly become available each year due to expiration of copyright. Interestingly, the IMSLP has recently become a more attractive depository for newly written compositions. Using the Creative Commons license, a great number of 21st century compositions have been uploaded by the composers themselves, thus using the IMSLP to sidestep traditional methods of publication.
IMSLP is a unique database. It is built like like a Wikipedia page, but with the functionality of a Google search engine. A sample search for instrumental solos (in this case trumpet) might yield a page like the image below. Keep in mind that these are only listed pieces in the public domain, meaning generally pieces from the last 50 years are not going to be available. Also IMSLP may not have scores or recordings for more obscure composers or works, because they are generally harder to access and have not been scanned into the database as of yet.
After searching for a list of solos for a given instrument, you might get a result screen that looks like the image below. From here you cn view the general metadata for a piece. Also the score and parts for the piece are listed, in different editions if applicable. If any recordings or video exist of that piece, they are also linked in this results screen.
You can also use the categories box at the bottom of the screen to search for other related works