The future progressive can be used in a number of ways:
1) For an action that will be in progress at a certain time:
At 2pm I will start.
At 2.30 I will be doing the exam.
Bt 4.15 I will have finished
2) For an action that will happen in the normal course of events:
I'll be speaking to her tomorrw. (This will happen anyway)
3) For assumptions about a present action:
Don't ring her now- she'll be having dinner. (I know what time she eats)