This is alot to answer, so I’ll just help you think of what to do.
Main ideas are the central message that you want to state or convey in your paragraph.
For example, write about how bad habits affect people.
Another example, write about how living at home affects your social life. Or how staying at home makes you feel better about certain things, like staying away from viruses from large groups of people.
Another example, write about how TV commercials persuade others to buy certain beneficial products, however, TV commercial can promote harmful products to viewers too. (Like cigarettes)
If you need any more help just comment below and I can help you think of something for each one.
Just remember: The main idea is a sentence that provides the subject for discussion; it is the topic sentence. It is usually supported by a list of details.