I bought a bullet-proof old singer sewing machine from Goodwill for $15.00, and did a bunch of practice sewing on scrap fabric. After that, I re-upholstered a bench seat in my old Chevy Truck. Some of those old machines are super strong and can go forever if properly adjusted and lubricated. Look at the underside of the machine ... if you see lots of heavy steel parts and connecting rods that remind you of the rods connecting the wheels on an old steam locomotive, that's a good thing. If it's heavy when you pick it up, that's a good thing. Pull the bobbin out of it, take the belt off the flywheel, and spin it over ... if it glides nice and smooth, that's good too. Make sure you get a machine with a zigzag capability. Most all home machines have that.
After the upholstery job, I made some stuff sacks, then a gore-tex bivy, then a goosedown quilt (based on the "Hungry Howie" design), then a couple of backpacks.
Take a look at http://www.backpacking.net/makegear.html, where you will see a lot of instructions on the left. It's also very helpful to look closely at other gear you have, and examine how it's put together. Soon, you will be able to see that you have to first sew this seam, then sew this other piece on top ... etc. In other words, you will be able to see how it is made and in what order.
To make a bar-tack, set your zig zag stitch width to about 80% of max, and your stitch length to very very short ... almost zero. Then run it on some scrap fabric, and you'll be amazed to see you've just done a bar-tack.
Get some $1/yard fabric from Walmart and just play with it ... practice different things and you'll get a LOT more confident as you go. Take your time and enjoy it. If you get frustrated and loose your groove, put it down, take a hike, and enjoy yourself. Be calm and relaxed while working on an item you'll love. Let yourself go, and you'll feel a "flow" of work coming from your hands. It's very rewarding.
Best of luck, and be sure to share your results here on the forum.