Algodoo

Look at the right fixjoint: you're fixing everything to the background. Just delete it
If you see well, you've already fixed the yellow polygon to the red box with a fixjoint. You only need to use one, or the fixjoint will fix the first object with the object that is behind the red box. In this case, the "object" is the background.

Calm down! No need to get mad. Just ask for help, and there will usually be someone here who will help you.

Thanks Linkage for explaining how to fix his problem.

to fix it, make a circle, right click or double click it, go to geometry actions, press glue to background, and the circle is fixed to the background! that is how!