My Aunt Sharon asked that question today.
I was always a city girl, as she knows, and now, here I am: living in the country, building sheep shelters and fence line feeders, shearing sheep and spinning wool. The Reluctant Farmer is a computer geek like me ... but at least he grew up in small town Saskatchewan, and had relatives who did a bit of farming. He, at least, knows how to fire a rifle. :)
Back to the original question: How do you learn to do all this stuff? The answer is: with a lot of help.
I have done a lot of reading: books like Barnyard in Your Backyard, The Western Canadian Sheep Producer's Manual, magazines like Mother Earth News and Countryside Magazine, and an awful lot of web surfing. One of the best resources is the wonderful online community at Homesteading Today, where you can ask even the most clueless of questions and get answers from generous folks who have been there, done that. There are people there who will patiently explain how to build a fence so it won't fall over, ease your anxiety the first time one of your ewes is in labour and you have no idea what to do, or talk you through the steps of handspinning even if you're not sure which end of the spindle to hold.
There are ideas all around us, too: I find myself slowing down to check out people's farm layouts, looking to see if there are features they have that would work for us. The fenceline feeder we have was inspired primarily by a plan I found online, but the thing that gave me the push I needed to actually build it was a farm not far from here that has something similar for their sheep. Seeing one in action made it really easy to imagine how well it would work here.
We also have a wonderful real world community, particularly our 4-H families. Everyone has shown great patience in helping a city girl learn how to do simple things like order the right amount of hay for the winter, catch a chicken, or trim a sheep's hooves. I'm sure many have laughed at our efforts ... but they've at least been gracious enough to do it when we can't hear them, and really, everyone has been very encouraging. After all, everybody learns somehow ... and not all of us grew up on farms. The 4-H kids did think it was pretty funny that I hadn't ever ridden in a tractor, and that I had no idea what it meant when someone said they were "graining their steer" (turns out it's like carb-loading: feeding a young lots of grain so he'd grow), but they seem to think it's pretty fun to teach a grownup how to do things.
Our 4-H leaders are a great help, too: our previous sheep leader taught us how to give a sheep an injection, loaned us equipment, and even gave The Boy bottle lambs to raise. She's always available if we have questions or need help - when we had a ewe with a troublesome delivery, she and her son dropped everything and came right over, and called in a local sheep expert when the problem turned out to be more substantial than it had appeared.
Other families have shared hay bales with us when we ran low, described methods of tightening fence wire or building gates, and told us where to find good deals on feed. We've had lots of construction help from neighbours, and we are tremendously grateful for all of it.
Hopefully, someday, we'll be able to give back to our community too.
The rest ... well, the 4-H motto is "Learn to do by doing", and that is really what we do. We try things, and they don't always work very well, so we tweak and try something different. Standing out in the pasture this past spring it became really clear where the hay ought to have been stored, and where the fences should have been, and where a fenceline feeder should go.
It's a long journey from city girl to shepherd, but I'm getting there, a little at a time ... and with a lot of help along the way.