+ regular verbs: have/has & verb+ed --> I have/ she has looked
+ irregular verbs: have/has & 3rd row of list ----> written, seen
- negation: haven't/hasn't --> I haven't looked, she hasn't taught
? question ---> has she started?, have they thought?
time expressions: already, for, yet, since, how long.
when we use it: action has started in the past and still happens