404 crawl errors for moved posts

I used to have a messed up permalink structure back when my website http://www.futurepocket.com was first launched, I also had a wp-forums installed but all that has been removed now — plus there are some deleted posts. Google however keeps trying to crawl these posts/pages and gives 404 errors, is there anyway to notify them that these pages don’t exist anymore? Maybe offer a 301 redirect to the main website? How would I set up the 301 redirect?