The Re-Volt Hideout

How can I download content packs and anything else? Everytime I download anything it does not appear in the game.

They need to be placed in the same way as you would download some custom track/car on a PC manually: unpack the downloaded files and paste the gfx/levels/cars folders into your folder with RVGL on Android. Easiest to do that is probably to copy-paste these 3 folders from PC to phone.