Hard to answer that one in a nutshell. Probably best to explain (or look up in a dictionary) the word 'too' to start with, as it crops up less than the word 'to' but is still quite common.
'Too' generally denotes an excess of something, eg you're driving too fast; or a lot of something eg you're too kind; or is a synonym for 'also' or 'in addition', eg I can dance and sing too. (I can dance. I can sing too.)