Single jersey is a structure knitted on one needle bed, with all needles knitting every row. This makes a light, flexible fabric that can have some transparency. The edges tend to roll in.
The canvas in the design app is made up of front bed single jersey by default. Single jersey can be knit both on the front bed (which looks like knitting in hand knitting) and on the rear bed (which looks like purling in hand knitting).
Open the stitch selector in the toolbar on the left, and select the stitches to create single jersey as below.
You can choose to knit on the front bed or on the rear bed.
Select Free edit, then pick the drawing tool you need (pencil, line or rectangle) and draw. See this video:
Below a detail of single jersey on the front bed (left) and on the rear bed (right).
Here are the recommended parameters for single jersey (nm7):
Stitch size: between 6 (quite tight) and 10 (quite loose)