I think (that)…

…だと思う

I think that it’s going to rain.

I think she is nice.

I guess (that)…

…かなと思う

I guess he is busy.

I guess we are late.

…だといいな

I hope you like the present.

I hope we can meet soon.

…かな？

I wonder if she is okay.

I wonder how spicy this is.

…かどうかわからない

I’m not sure if he is coming to the party.

I’m not sure if I can do it.