Sleeping

How do I get my 4 week baby to sleep on his own. If I put him down he can sleep for min 5 minutes to max 20 minutes before screaming bloody murder. I'm at this point where I co sleep because he can easily sleep 2+ hours on my chest. I need advice, tips on how to get him to sleep in his own bassinet. I miss sleeping with my partner and having that closeness and I don't want my son to get used to sleeping with me. I want him to be able to sleep on his own. How did you mommies do it?