How old is the snake? A baby or an adult?
Generally, after you get a new snake, you need to give it a week to settle in and relax. THEN you feed it a meal about half the size you'd normally feed it. Then let it digest for two or three days, THEN you can start gentle handling!
Pretty much all cornsnakes rattle. What it means is "leave me alone" or "you have startled me" or something like that. It doesn't mean "I am going to bite you." There _is_ a chance that the snake will bite, but it's not likely, especially if it is an older snake. Don't worry- if the snake _does_ bite, that does not mean that it will _always_ bite. He's having a very stressful period in his life right now! And a bite from a hatchling is _nothing_; it feels like Velcro. The worst the biggest adult can do is make a couple pinpricks! Yes, it will startle you if it happens, but it doesn't really hurt.
So, after the settling in period, you will want to pick the snake up to move him to his feeding container. Just reach in, don't hesitate, scoop him up. If he's a little baby, be very careful not to drop him! Hold him just tightly enough that he can slide slowly through your fingers, but not tightly enough that you are pinching him or restraining him from moving at all, and do not hold him by the neck or near the tail- they really do not like that. Let him move from hand to hand, or keep him cupped in your closed hand.
If you have an adult, pick him up in a clump and then hold him well-supported and let him wind around your hand. You'll get used to him, and he'll get used to you. It just takes a little time.
After he's done digesting his first meal, you can start gentle, short handling periods. I'd suggest taking him out and sitting down to watch a half hour TV show with him- holding him cupped up close to your body, or coiled around your hand, but not the center of your attention. Let him relax. Do NOT set him down anywhere or let him fall!