Here's how it works:
* Present Perfect Tense: This tense describes an action that started in the past and continues to the present, or has an impact on the present.
* Formation: "Have" (or "has" for singular subjects) + past participle of the verb.
* Past Participle of "write": written
Example:
* I have written three letters today. (The action of writing started in the past and is completed, but it has an effect on the present because the letters exist.)