Study the example below:
It’s 6.30 in the evening. Mary and Stuart are cooking dinner. They are making pasta with tomato sauce.
Half an hour from now, Mary and Stuart will be eating dinner.
Two hours from now, they will have finished their dinner.
Future Continuous (will be doing something) is used to talk about an action in progress in the future.
eg. This time next month I will be swimming with the dolphins in Zanzibar.
Future Perfect (will have done something) is used to say that something will already be complete before a time in the future.
eg. We are late. The football match will have started by the time we get to the stadium.