The adverbs also, as well and too have similar meanings, but they do not go in the same position in sentences.

Also is usually used with the verb. Too and as well usually go at the end of a sentence or clause. Note that ‘as well’ is not very common in American English.

He not only plays; he also works.
He was fat, and he was also short.
He not only plays; he works as well.
He was fat, he was short as well.
He not only plays; he works too.
He was fat, he was short too.

The adverbs also, as well and too can refer to different parts of a clause, depending on the meaning. The exact meaning is usually conveyed by stressing the word or phrase that also/as well/too refers to.

In short answers
As well and too can be used in imperatives and short answers. Also is not usually used in these sentences.

‘She is pretty.’ ‘Her sister is (pretty) as well.’ (More natural than ‘Her sister is also’)
‘I have got the invitation.’ ‘I have too.’ (More natural than ‘I have also’)

Note that in informal speech, we often use ‘me too’ as a short answer.

‘I am going home.’ ‘Me too.’ (Less formal than ‘So am I’ or ‘I am too’)

When used at the beginning of a clause, also can refer to the whole of it.

It is a small house. Also, it needs a lot of repairs.

In a very formal style, too can be used immediately after the subject.

I, too, have been in such situations.