I have a rude 4 year old boy.?

My son talks back. I am too lenient as a parent, and I am working on that. How should I respond when he says, rudely, "No, I don't want to!" or some other rude comment? Typically, I just correct him by saying, "you are doing it anyway" and I make him do it. I also struggle with having him sit properly at the dinner table. He tries to put his feet on the table or he pushes his plate away. I get annoyed and push his feet down. It turns into a bad time because I get mad and sit right next to him and basically feed him. I need some common sense answers please. I had been clinically depressed and I am now on medication, but I still don't know how I am supposed to respond. When I was depressed, I ignored him too much. I am doing better with spending time with him now.