How do you cook with peppers and onions?

[trunolimit]

Do I jut toss them in with what ever I'm cooking or do I wait a bit? I want to add some flavor to my meats and I was thinking about adding some bell peppers and onions but I don't know if I am suppose to wait until the meat cooks a bit then add in the peppers and onions or do I add them in first then cook the meat in with them.

This goes for chicken too. I noticed that my sister and mom add peppers and onions to everything and it smells and taste a lot better than what I make. When my sister cooks the house smells amazing but when I cook it smells bad.