Knitting is basically two stitches, knit and purl. There are some patterns that are all garter stitch (all knits), but the majority use a combination of both so yes, I'd say you should learn to purl.
**Please provide a pattern link and/or name if possible and as much information as you can when asking questions so we can help you better and more quickly.
Yes, unless you plan on doing nothing but garter stitch for the rest of your knitting days.
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Zina
OTN: Eyelet Chemise in Handmaiden Sea Silk (colorway: Midnight). Still. And a purple Donegal Tweed set of fingerless mitts, to try out my new Hiya Hiya interchangeable needles.
Latest FO: A shrug for an Anthropologie swap in beautiful Casbah sock yarn, in Cedar, a dark green semi-solid, my own pattern. Also a quick Noro Silk Garden neckwarmer for my friend Aideen, in a vine lace pattern.
Check out my photoblog: Photobella
Well, I've wrestled with reality for 35 years, Doctor, and I'm happy to state I finally won out over it.
--Elwood P. Dodd