At some moment in the future, I'll be in the middle of doing something.
We indicate some moment in the future (like "when you come" or "at ten o'clock tomorrow") and we say that at this moment there will be some activity going on. This activity will start earlier in relation to this future moment and it will go on after it. This is the main case when we use the future continuous, or the future progressive tense.
Examples
When the boss comes in the office room, everybody will be sitting at the desks and working hard.
At this time tomorrow, I won't be working. I'll be packing my suitcase.
When we arrive at Sarah's place to pick her up, she won't be ready to go. She'll still be choosing which dress to wear.
In the next episode, we'll be exploring the most beautiful places in Cornwall.
Do not forget that Continuous tenses are not normally used with stative verbs (verbs that express feelings, senses, intellectual processes, thoughts etc.).