“I'm so out of it this morning.”
You accidentally sent your coworker the wrong file. He points this out, and you apologize. You explain that you've been making a lot of small mistakes this morning, and can't focus well.
I'm so out of it this morning.
"This morning" means the morning today. You can use it to talk about something earlier or later:
What time did you leave this morning?
What time are you leaving this morning?
"This afternoon" and "this evening" work the same way:
I had coffee with Mr. Hernandez this afternoon.
Hey, are you doing anything this evening? I was invited to this party and I was wondering if you'd like to join me.
Being "out of it" means being tired, sleepy, distracted, or not focused.
You use "out of it" like this:
You seem kind of out of it today.