'Too' and 'also' have the same meaning. 'Too' usually goes at the end of a phrase. 'Also' can go in different positions. 'As well' has the same meaning, and usually goes at the end. For example: Ana speaks Portuguese. She speaks Spanish, too. Ana speaks Portuguese. She also speaks Spanish. Ana speaks Portuguese. She speaks Spanish, as well. 'Either' is different. You use 'either' in a negative sentence. Ana doesn't speak speak Japanese. She doesn't speak Chinese either. We often use 'either' in short negative answers: A: 'I can't do this homework' B: 'I can't do it either. It's too difficult.'