Maths teachers who co-teach/act as a supporting teacher, what do you do?

As a uni student studying to be a maths teacher, I'm doing some work similar to SLSO in maths classrooms where I support a maths teacher in bottom maths classes. I know at some schools with struggling maths classes, maths teachers can take on a co-teaching and supporting role so that there are two maths teachers in the classroom. What does this look like for you? What are the best ways to support the main teacher?