I cant do anything until I know how to set how long the animation is going to be, Please respond someone!

Normally, you can simply go ahead with your animation until it has a number frames required for your scene. (fps x time duration).
Also, if you wants a visual duration reference in timeline, you could create a drawing element with no contents, and set exposure (right click /set exposure) to fill all the scene duration. The playback duration will be as long as you had set this exposure. You can modify the playback segment selecting the free playback option, and moving the black diamonds to the desired playback segment (right click on the brackets area in timeline to show menu). Hope that helps you.