Learning basic sewing skills is never a bad thing. Knowing how to patch a hole in a pair of pants or stitch up a tear in a sleeve are valuable skills, especially if there comes a time when clothes are not so plentiful and we need to repair what we have when they start showing some wear. I'm kind of a sewing nut. It is very therapeutic. I enjoy the creation process. I do not enjoy picking seams that were sewn wrong, but that's another story. I enjoy sewing.
I pick up fabric at fabric store sales, online, and from thrift stores and yard sales. Because we do reenacting and make clothes for that, I try to stick to stocking fabric made from natural fibers--cotton, linen, silk, wool. I stay away from polyester, rayon, etc. One reason to stick to natural fibers besides being able to use them for our reenactment sewing is that if you're cooking over a fire and your clothes catch a spark, they won't melt and stick to your skin. If you're a welder, you know what I'm talking about.
Sewing would be an invaluable skill in a TEOTWAWKI situation. But it also could come in handy now. Because I can sew, I've been able to make my own curtains, cute pillowcases, and custom fit clothes for reenacting. I repair sweet husband's work jeans so he can keep working in them and snug up hand-me-down pants to fit my skinny kids. I've made my own maternity Wrangler jeans, Halloween costumes, and cute, modest skirts and dresses for my girls. Our sewing machine has paid for itself many times over.
Right now, it's generally cheaper and easier to just buy clothes from the store rather than buy fabric and make your own clothes. That is, unless you're looking for something in a particular color or style that isn't "in" this season. If you want to learn to sew, I'd suggest starting with a small project with straight edges--curtains or a pillowcase. Maybe a hotpad. If you don't have access to a sewing machine or want some hand stitching practice, hand stitch a patch on some old jeans or some embellishment on a handbag or jacket. Then move up to something a little more complicated. There are some very basic patterns out there for dresses, skirts, lounge pants, etc. Yes, it may be a tad more expensive to buy the fabric and sew it yourself, but you're learning a skill AND you get to pick your fabric and make it just how you want it.
Most of my clothes sewing is for our reenactment hobby. Most of the patterns I own are for that also. This is one area it is almost always less expensive to sew your own than to buy pre-made outfits. And I guess if the world ends and clothes get hard to find, we can always dress colonial. ;)
So give it some thought. Pick up some needles and thread, borrow a machine from a friend, maybe get some advice from a mentor and try your hand at sewing something. :)