I have been challenged by two players to a game of chess with me being black and I want to except their challenges but I am new to this website and I have been puzzling for several days now on how to indicate that I except their challenge when they haven’t yet made their first move. If I am white then I can indicate that I except the challenge simply by making the first move but how do I get the game started when I am black?

It's up to white to start the game by making the first move.

You can send them a message, but other than that you as black can only wait.

If you get tired of waiting just delete the game. It will not count for you or them, as there have been no moves.

I remember when I first joined, the site suggested a couple of people I might like to challenge. That might be what's happened here. Looking at their profiles I see they registered and then never moved. If I were you I'd delete the games and then start an open invite or something.