I guess it’s different depending on the platform you use. In traditional writing, I usually use italics when it’s a conversation and the person is thinking something while another person is speaking. For example:
“Maybe we could have coffee together sometime,” he said.
I tried to hide my excitement. Was he really asking me out? Yes, of course! How about tomorrow? I wanted to say. But trying to appear as cool, calm, and collected as possible, I said, “Sounds great! Let me know when you’re available.”
Now, on Episode, you can show a character’s thoughts in a thought bubble. You just have to put the text in paretheses.
(OMG! I can’t believe I got chosen for the cooking competition!)