Hi, MeeMee, this is a great project to expand your skills. Learning to read and interpret knitting patterns is an adventure.
Dec Row (RS): K 1, k2tog, k to last 3 sts, k2tog, k 1 – 23 (29, 35, 41) sts.
You'll Knit 1 stitch, then K2 tog. (you said you found the video, that's great) then just keep knitting across until you have 3 stitches left.
"k to last 3 sts, k2tog" I assume it means knit to the last 3 stiches then knit 2 stiches together but I am unsure. I also don't understand the -23 sts part.
You're right. When you have 3 stitches on the left need, do your dec (K2tog) and knit the last stitch. -23 means you'll now have 23 stitches. You were doing better than you realized.
You can't knit the left sock first. Ever.