Picking up stitches sounds intimidating but let’s work through it! The following example is a sock but the principles are the same when picking up stitches from stockinette no matter the project.
::: how to pick up stitches :::
To pick up stitches you need the right side of your work facing you (the knit side).
Step 1: Insert your needle into the stitch or between rows (from RS to WS)
Step 2: Loop the yarn around your needle (at the back of work)
Step 3: Pull the loop through to the RS (using the needle tip, as though you were knitting a stitch)
Now you will have a stitch on your right hand needle. You have picked up a stitch!