It will take a bit of time, but I'd start with a little grain in a pan. Just put it down and they'll come investigate. Stand nearby (but out of their flight range) so they get used to seeing you and associate you with the goodies.
If you have some corral panels or a pen, get them used to coming in there for their grain. Give them a flake of hay there also. I wouldn't lock them in there initially. After they're comfortable with this routine (keep it consistent as long as needed), you can shut the gate while they eat. Then open it to let them out. No sudden movements, no loud noises.
It will take time, but they'll soon start to sniff your hand (them inside pen, you outside). Move very slowly and quietly. Talk to them. Sooner or later, they'll be willing to take a treat from your hand and that's a big step for them.
If you're going to eventually butcher these guys, you will feel bad having made friends with them and it's best not to name them. If you keep them as pets, you'll progress to touching them with your hands, then brushing them, etc. I'm sure there are faster ways to do this, but I prefer the slow method (I don't move as quickly as I used to). Having "tame" cattle makes it far easier to apply fly stuff and pour-on dewormers. The ones that are halter broken don't forget what they've learned even if it's a few years since they learned. All the same, be careful and don't get injured; they're bigger and stronger than you are and can kick in all directions (even some calves).
