Okay I think I slightly understand something
Maybe a real-life example would make more sense: let's say you want to talk to a distant friend by sending them a letter, so you write one and then drop it in the mail box. What would you do afterwards? Would you sit down and eagerly wait for a letter from them to come back, or would you go cook yourself a meal and go about your daily life as normal? Concurrency would be you cooking a meal after you've left your letter in the mail, while parallelism would be you doing two things at the same time, like trying to call your hair stylist as you're cracking two eggs over some rice in your frying pan