If you run it alone (no one other than big miner factories do that) then if/when you hit one, you get (currently) 6.25 BTC. If you don't (and when you are running one miner it is very unlikely you will) you get nothing.
Most people with less than let's say 2000 miners join a pool. In a pool, when someone in the pool hits, everyone in the pool gets paid proportional to the amount of work they put in during that period.
Sounds like you could rack up a lot of expense in computers and electricity and never make any money...