When you work a Trellis Stitch you create the trellis-like effect by slipping stitches and then pulling those loops over a stitch in a later row. When worked in a pattern it creates a deceptively complex looking fabric although it’s very simple to create!

To start with you work slip stitches for 2 rows (or rounds) across 3 stitches. This give 2 long loops of yarn across the front of the work like this:

Now you knit to the middle of those stitches:

Next you take the tip of your right needle and lift both of the yarn loops onto the needle from below:

Now knit the next stitch:

Lift the yarn loops over the knit stitch to create your trellis stitch:

This is what the completed stitch looks like: