How do I change the background color for a specific element?
Use the property background-color which specifies the background color of an element.
Can I use any image from Google within my design?
NO, never google search an image and use it without knowing if you can use it or not. The best thing to do is find a free online stock photo site. One that I like to use and that is 100% free is https://www.pexels.com/.
What is the best output for my video?
When selecting and output for your video the best and most popular container to use among editors and myself is h.264. It supports both standard and high definition footage.