Where to start... Please help

New to the program and developing games. When starting a new project after you have your ideas what specifically would you start making first, maps, characters, etc.? I have my idea but I dont know how to get started, what do you all usually start making first?

Try starting with prototyping. use cube and other simple shapes first to see if what you want to make works and is fun.

If you are happy with your prototype then it is time to decide what are the most important parts of your game. Make the most important parts first. When you finish those you can add other less important.

So if you make a basketball game for example.
First, you use cubes and other simple shapes to test it.
Then you make the most important parts. The net, the ball, the players etc,
When these work you can start adding background objects, Sounds, effects, etc.