De dicto and de re are two different way to talk about something.
De dicto is when you talk about something in a way that implies it's true even though you can't know for sure. For example, if you said, “I hope it rains tomorrow," that's de dicto since you don't know if it will actually rain.
De re is when you talk about something as if it is actually known or definitely true. So if you said, “It's raining today," that's de re because it's a statement of fact that you know for sure.