| To express a decision: |
| I'll have the steak, please. |
To express doubt, uncertainty, speculation: |
| I hope it'll be fine for the barbecue tomorrow. |
In sentences with "If...": |
| If I speak to her, I'll tell her. |
In sentences with "When...": |
| When I finish this session, I'll turn off the computer. |
I'll have the steak
The standard way of ordering in a Restaurant.
Note the use of "Have" with the meaning of "eat"...
doubt, uncertainty, speculation
For other examples...