English question, please help?

I am ripped: I have just worked out and my muscles are feeling good (I think). After that 3 hour training session, I feel ripped.
Opting out: choosing not to. He opted out of going on the picnic
Tuned in. I can't explain it! He was tuned in to what was going on in and around the town.
You must keep your head: you have to stay calm.
'If you can keep your head when all about you
are losing theirs and blaming it on you' ~ from If, by Rudyard Kipling

'I am ripped' generally means 'im really muscly' or along those lines anyway
an example.. I'll use my brother's saying 'Man I'm ripped. Been working out at the gym for a while now'
'tuned in' can be someone asking you if you're listening- example 'Are you still tuned in?'
or it could mean are you up to date on something.
'you must keep your head' is just another way of saying stay calm or dont panic- people tend to say it before someone does an exam or has a job interview.

i hope I helped!

"I am ripped" means one person is muscularly built.
Ex. "Joe, my Navy friend was ripped when he came back from basic."

"Opting out" means one decides not to go through with a decision.
Ex. "Sorry Lisa, but I gotta opt out of going to the movies tonight, due to my dad being sick and all."

"Tuned-in" means listening in to a conversation, or watching a certain TV show.
Ex. "Maggie could help but tune-in to the conversation of the people sitting beside her."
Ex. "American Idol will be canceled forever. Tune-in tonight at 11 PM for more details."

"You must keep your head" means to keep your cool or demeanor.
Ex. "Hey, keep your head man! She's just angry. Don't worry, she'll get over it."

Hope this helped!