Cheers can mean a few things. It's most known for being something you say before taking a drink. It's a drinking toast in this sense. In British English cheers can mean goobye! or cheerio! It can basically mean "Thanks!" However, I think instead of thanks, I think it's more of an expression of good wishes. One thing is for sure, it's used as a very friendly expression.

It is similar to thank you, but only some groups of English speakers would use it. Cheers tends to express "I have acknowledged you, this transaction is finished now". You should use 'thank you' to express gratitude as that is the universally accepted term.