'Also' Vs 'As well' Vs 'Too'

These three expressions have similar meanings, but they are used in slightly different ways in sentences. 

1. As well and too

These normally go at the end of a clause. 

S/he not only singes; s/he plays the piano as well. 

I was Thailand last summer too. 

'As well' and 'too' can refer to the subject or to other parts of the sentence, according to the situation. Consider the following: 

Mr. Bean teaches skiing as well. 

This could mean three different things: 

a. Other people teach skiing, and Mr. Bean does as well. 

b. Mr. Bean teaches other things and skiing as well. 

c. Mr. Bean does other things and teaches skiing as well. 

The situation normally makes the meaning clear in cases like this. In spoken English, the meaning is also shown by the emphasis (on third). 

'Too' (but not 'as well') can be placed directly after the subject. This is rather formal or literary. 

I, too, know where he is to be found. 

In an informal style, 'too' is often used after object pronouns in 'short answers'. 

'I've got an idea!' - 'Me too' (In more formal English: 'So have I!' or 'I have too!')

2. Also

In an informal style, 'also' is less common than 'too' and 'as well'. It is very common in written English. It does not come at the end of the clause but is normally put with the verb. 

Mr. Bean also plays the guitar. 

I've also read her other novels. 

'Also' can refer to any part of the sentence: 

Harry was at the party, and Fred was also there. 

I like classical music, but I also like jazz. 

However, 'also' most often refers to the part of the sentence that comes after the subject. So Mr. Bean also plays the guitar probably means 'Mr. Bean plays the guitar as well as other things', not 'Mr. Bean plays the guitar as well as other people'. If you want to say that you have had too, but probably not I also have done that or I have also done that. For the same reason, we don't say 'I also' in 'short answers'. To express the idea that something is exceptional, we use 'even', not 'also'. 

Even when he was every old he used to go for long walks (Not: Also when...). 

You shouldn't be rude, even if you are very angry (Not: ...also if...). 

Note the use of 'also' as a 'sentence-adverb', at the beginning of a sentence, with a common. 

Old cars are cheaper to buy, but they tend to use more petrol. 

Also, there is a greater risk of accidents. 

3. Note that 'also', as well' and 'too' are not normally used in negative sentences. Instead, we used 'not...either' or 'Neither/Nor'... Compare the following: 

He's there too.     He isn't there either. 

I do too.     Neither/Nor do I. 

I also want some coffee.     I don't want any coffee either. 

I like you as well.     I don't like you either.