It’s nice if you can read sheet music, but it’s not a requirement to participate well. We sometimes work with it, or with guitar tabs, or chord charts, or with lyrics without music, whose melody we already know or get.
Of course, some people are used to working with sheet music. It’s not very difficult and they can explain it to you if it’s convenient. Working in groups, as we do, makes it easier.
You can also download and copy sheet music, chord charts and lyrics.