Modals are quite tricky even for advanced speakers to get right. Getting them wrong can communicate the wrong impression. You need to really practice them. They are used a lot in speaking and they frequently come up in Task Two writing.
Look at these essay topics.
1. What changes will the world see in technology over the next 25 years?
[DEGREES OF CERTAINTY]
Over the next 25 years we WILL / MAY / MIGHT / COULD see …
2. How can governments help citizens emerge from poverty?
Governments COULD … / SHOULD / MUST
3. If family size declined to just one child per couple, what problems could emerge?[HYPOTHETICAL SITUATION]
There COULD / MIGHT / WOULD /