1. Form
   1. Subject+have/has+ past participle
      1. Regular verbs: -ED
      2. irregular Verbs: 3rd column
2. Useful time expressions
   1. For/Since
   2. Just/Already/yet
3. Uses
   1. Unspecified past experience.
   2. Unfinished situations. Started in the past and continue.
   3. Finished event that shows results in the present.
4. "I have been to Paris." "Today hasn't finished" "It has rained a lot"
5. Pay attention to the kind of verb!