ALSO:
- More formal
- Commonly used in writing
- Used before main verb and after the modal verb
E. g. He is a singer and also an actor.
TOO
- Used in common spoken and informal English
- Used at the end of a sentence
E. g. I'd like to come too.
AS WELL
- More formal than 'too'
- Used at the end of a sentence.
E. g. Are you coming as well?
The only difference is in their placement in the sentence. 'Too' and 'as well' are used at the end of a sentence. ('As well' is more formal than 'too'). 'Also' usually goes before the verb or adjective.