Oh, here I'm going to show you how to make an NPC say different sentences nearly everytime you talk to him...
Step 1. Make an event.
Step 2. Make a variable called talk randomizer.
Step 3. Set talk randomizer to random 1~4.
Step 4. Make a Conditional Branch. Make the condition "talk randomizer is equal to 1".
Step 5. Make a Conditional Branch. Make the condition "talk randomizer is equal to 2".
Step 6. Make a Conditional Branch. Make the condition "talk randomizer is equal to 3".
Step 7. Make a Conditional Branch. Make the condition "talk randomizer is equal to 4".
Step 8. Your Event Commands list should look like this now...
Step 9. In each Conditional Branch just put in whatever you want the NPC to say or do.
End result...
If you have any questions just post.
I hope it helps!
EDIT: You can also put all this in a Common Event and simply call it through an event when you need it.
Mr_Wiggles