I bought this for my husband when he started going to Mass before he converted
It's a little bit difficult to get the hang of off the bat, because there are parts you gave to skip [like for example, 4 different Eucharistic prayers, so you have to skip the 3 that aren't being used. For Sunday Mass it should always be the first one]
But, wear something business to business formal, sit in the back, and just observe. You don't have to participate the first few times you go. My husband wanted to, because he personally felt like it was important, but it isn't mandatory.
You could, if you don't want to spend money, download the ibreviary app instead, however my husband said he didn't like being on his phone during Mass, and felt like it was a little clunky. There are other people who don't feel this way, that's just what my husband said.
If you're concerned about the quality of the Mass, you can look on reverentcatholicmass.com to find Masses in any language that are more conservative/reverant. From there, you can check a parish [church building] Mass times to see what time works best for you :)
Pretty much no one will be paying attention to you, except maybe the ushers in the back, but tbh they don't usually say anything. The more reverent the church, the less they are likely to notice you.
My husband also found it a lot more helpful to read a couple different 'A Minute In The Church' books, specifically the one about the Mass and the one about the Eucharist, so he could more understand why we do things and the flow of Mass. It can be a little overwhelming the first time, just because everyone will know what to do, but it shouldn't take too many times of going to start getting the hang of it. I think it took my husband a month? So going 4 times. And 1 of those times he had traveled to a different state in order to visit his family, and he still went to Mass. He wasn't familiar with any kind of service, except for more of those rock-concert type protestant services, that he had been to occasionally growing up with friends.
Also, if you're able to go to my wordpress/FAQ on my desktop blog, I link to all these things and more :)