ComCat stands for "Commonwealth Catalog" and is essentially a catalog of all of the public libraries in Massachusetts. If you can find what you want in here and request it, it'll be sent to the library circulation desk and you'll be emailed when you need to pick it up. It's a great way to utilize public libraries in MA if you don't have time to go to one or don't live in MA.
(This is kinda like interlibrary loan except different, as these books only come from Massachusetts libraries vs. any library in the world like a typical ILL request)
In my opinion, the interface isn't as intuitive as some others. The search box at the top of the page is automatically searching for "keyword" (like comics or superheroes etc.).
If you want to search for something else, like a specific creator or title, click the check box between the world and the stack of coins (or whatever that is) and select the thing you want to search by. Remember, if it's a phrase like someone's full name or a title, put it in quotation marks so the catalog knows you need those words together. It'll really help here!
The results page can feel chaotic! If you don't see the item you're searching for immediately, use that left column to try to narrow the results.
When you find something relevant, click the cover photo. It'll just give you a brief summary of the libraries that own it and the option to request it.
Click on the cover photo again to get more details, if that's what you're into. The subjects can often be insightful and the "info" can sometimes include a description of the story.
When you click "Request This Item," it'll open a little window and ask you to confirm info like the latest date you need it by.
You'll get an email when it arrives and all you have to do is stop by the library's circulation desk to get it.