I recently had to learn how to do a garter tab cast-on for a cardigan I am knitting. Though there are tons of tutorials on how to do this seemingly easy technique, I found the majority of them to be too complicated and not clear enough for me. Once I finally understood how to do the garter tab cast-on, I decided to make a short Instructable---hopefully this will save others hours I'm embarrassed to admit I spent trying to figure this out. This Instructable also includes a very helpful pro-tip.
Step 1: BoM
Step 2: Cast On
Cast on 3 stitches (or however many stitches your instructions say to cast on).
Step 3: Pro Tip
Put a stitch marker on each of the stitches to help keep track of them. This is a very helpful trick and makes this so much less confusing later.
Step 4: Knit
After placing the markers, you will knit however many rows your directions say. Mine said 6, so I knitted 6 rows.
Step 5: Pick Up Stitches
The next row is where you pick up the stitches along the garter tab edge by sliding the left needle into the edge of the rows you knitted (pic 1) and knit 3 stitches (pic 2). You'll have 6 stitches on your other needle.
Then you will knit the original 3 stitches from the cast-on for a total of 9 stitches on your right hand needle.