Beginning a Simple Double-Knit Project
First, start by casting on the requisite number of stitches (42 for the Pawprint Blankie, for example) with both colors of yarn held together.
Your completed cast-on row may look a little... jumbled, but that's okay.
Now, let's start knitting! Turn the work around, and slip the first stitch of BOTH colors purlwise, with yarn in front.
Bring both strands of working yarn back behind, between what you just slipped and the stitches about to be worked...
Now you're ready to begin working your first double-knit row! Keeping both strands behind the work, knit the MC loop from the cast-on stitch using your working MC strand.
(For this tutorial, MC is green, and CC is cream.)
Now bring BOTH working strands to the front, and purl the CC loop from that cast-on stitch. This is the first stitch on the reverse side of the work.
Keep working this way, knitting the MC and purling the CC, always keeping both working strands on the same side of the work, and soon the double-knit fabric will begin to form!
^ There's a good start. If you have any more questions about double-knitting, feel free to ask!