I recently started Game Maker. My character keeps falling through the ground. Can someone explain this as simply as possible?

I haven't used that program in years, but whenever I got lost with something our teacher gave us I would just go onto youtube. Lots of helpful tutorials on there if you haven't looked already. If you're planning on stepping into the big leagues and becoming a real game designer though you have to get rid of the 'simply as possible' attitude. When it comes to game design you can't always expect simple solutions. It takes time and patients to understand problems and address them correctly.