Your agency may send you a shortlist, a few acts they think fit, so you can pick rather than being told.
Have a look at each profile before choosing. Photos, past gigs and any technical requirements are all there.
If none of them are right, say so and ask for different options. That's much better than picking the least-wrong one and being disappointed on the night.
Once you've chosen, the agency offers the gig to that act. It's confirmed when the act accepts; a shortlist choice isn't a booking on its own.