myself
The Italian equivalent for English 'myself' is 'io stesso'. It is used in the same way as in English: to refer back to the speaker. But, unlike in English where 'myself' is used for both singular and plural, in Italian different forms are used for plural.
I did it myself.
This sentence can be used when you want to emphasize that you performed an action personally, by yourself, without anyone's help.
I myself could not believe it.
This phrase can be used when you are in a situation so extraordinary or unbelievable that, even being the person directly involved, you find it hard to believe.
I cooked the dinner myself.
This sentence can be used when you want to emphasize that you were the one who prepared the dinner, without any help.