It's very colloquial for 'thanks' - but it's used in a very informal way. And not in place of 'thank you' as such.
For example, "Can you please pass me that cup?...*person hands over the cup* ta!"
"Thank you for coming today." - You wouldn't ever say, 'ta for coming!' it's just too informal, unless it's with a very close friend or something, but you'd still likely say, "Thanks for coming!"
Another place we'd say it is like, "Can you grab some milk for me on the way home? ta.."
Sort of inserted at the end of a request - again, between maybe a mother and son, or close friends, as a pre-emptive thankyou.
It's very complicated actually - but i wouldnt reccomend actually using it until you recognise when others do, as if used inappropriately, it'll really stand out. The same goes for most colloquial terms- understand them completely before attempting to use them.