Point of view
Question: If I use third person won't it be awkward? I mean, if I know exactly how the other person feels. I want it to sound real. Suppose I use third person like, "She wondered why he had suddenly shown up" or "He pretended to be fine but he knew he wasn't going to survive." So is it okay of I write like that?
There's nothing wrong with either of those sentences. The issue is whether you are writing third person limited vs. third person omniscient.
"Limited" means that you are writing from one particular character's point of view. The reader only learns that character's thoughts and feelings. The main character cannot read minds, so the only things we learn about other characters are what the main character observes or already knows. We we may learn how other characters look, what they say, their gestures, facial expressions, etc., but we cannot know their thoughts or feelings any more than the main character could. Main characters will often infer things about other characters, but their inferences are sometimes wrong.
With omniscient narration, on the other hand, you have a narrator who can change perspective and sometimes report the thoughts and feelings of more than one character.
The downside of this technique is that the reader feels less intimacy with any one character. It can be quite jarring to "jump heads" within a story. Readers enjoy the illusion of being one character, and that illusion is spoiled if they suddenly find themselves in another character's shoes.
The advantage of omniscient is that it offers an objective view of the entire story world.
Limited narration is far more popular today, but the choice is yours.