You just have to get lucky enough to find one and then have a lasso, whistle, and use treats and pets to to capture it. Its mostly luck but since a lot of this game is broken and now ran by one awful person its probably broken too or it will break at some point. But its a lot of chance

I'm still fairly new so I'm not much help. All I know is for me, it's been very hard to catch wild horses XD Idk, maybe I'm not doing it right but I often run out of lassos, whistles and treats. There's a bit of info here about wild horses! But, I do believe a lot of it is up to chance XD

The ones that work by far the best for me are the molasses and other crafted treats.. the other tools are often pretty iffy although they may work if you run out of treats. Takes a bunch! I’ve learned not to try catching unless I’ve got a good stock pile of treats..otherwise you waste them all.