Future perfect tense describes actions that will start in the future and end at a specific point. It is formed by adding the helping verbs 'will have' plus the past participle of the verb. It is different from simple future, which is formed by adding 'will' to the present tense form of the verb.
Michael will open the basement door. Two glowing red eyes are going to look up at him out of the darkness. He will jump. He will fall down the stairs. Becka, his Siamese cat, is going to meow plaintively and wash his face. Her pale blue eyes will still glow red in the reflected light from upstairs.
it is saying in the future they will do something
