“I hope he's able to fit in at his new school.”

Your son is starting at a new school next week. He's nervous because he doesn't know anyone who goes to this school, and he's not sure whether he'll be able to make friends there. You're concerned for him too. You say to your husband:

I hope he's able to fit in at his new school.

I hope (clause)

English learners often confuse "I hope" and "I wish". Use "I hope" when there's a good chance that something might happen. One way it's used is to say what you want to happen in the future. For example:

I hope we win tomorrow night.

In the example at top, there's a good possibility that your son will be able to fit in. So you use "I hope..."

"I wish" is used to talk about things you want that aren't true or very unlikely. So if your son was already unpopular at school, you could say:

I wish he could fit in a little better at school.

Another point about using "I hope" is that you follow it with the present tense of a verb, even when you're talking about the future. So you say "I hope we win", not "I hope we'll win."

fit in (somewhere)

When you "fit in" somewhere, it means that you're accepted by people and able to make friends there. People are usually concerned about "fitting in" at work or at school.