There is no difference in meaning. They both mean "up to the time when (something happens)".
"until" is an all-around common word, while "till" is slightly more formal, I think.
When in doubt, just use "until" and you'll never be wrong.
- Keep working until you get what you set out for = Don't stop working before you get what you want.
Here's a verse from a Beatles song.
- There were bells on a hill
- But I never heard them ringing
- No, I never heard them at all
- Till there was you
* I never heard them until/till there was you = Once/After there was you, I started hearing them.