Present Perfect
I've been studying the present perfect.
Present perfect is an action from past to present.
It almost seems too simple.
Present perfect uses 'for' and 'since', but doesn't use 'ago'.
'For' is duration.
ex) I've been in Tokyo for two years.
'Since' is from particular point to present.
ex) I've been in Tokyo since January.
'Ago' uses simple past.
ex) I lived in Tokyo two years ago.