Present Tense (or Simple Present) refers to an action as it takes place; for example, "I write."
Present Perfect (or Simple Present Perfect) concerns action that began in the past but is completed in the present; for example, "I have been writing."
Present Continuous (or Simple Present Progressive) indicates action that is happening in the present but is ongoing, such as "I am writing."
Past Tense (or Past Simple) identifies an action that has occurred and is now complete, such as "I wrote."
Past Perfect (or Simple Past Perfect) refers to an action that began and was completed in the past, such as "I had written."
Past Continuous (or Simple Past Progressive) identifies action that began and was continuing in the past; for example, "I was writing."
Future Tense (or Future Simple) looks ahead to action that is yet to take place; for example, "I will write."
Future Perfect (or Simple Future Perfect) describes an action that is still to take place as though the action were completed; for example, "I will have written."
Future Continuous (or Future Progressive) describes continuing action that is yet to begin; for example, "I will be writing."
For simplicity, the examples given are all first person singular, but the same rules apply whether the noun or pronoun used with the verb is singular or plural. "We will have written," "They will have written" and "You will have written" are all examples of the future perfect tense.