How do you join 2 different cast on threads

I am trying to make a poncho that has one color for the main body and a smaller block of another color on the bottom. It is supposed to be for beginners - which I am!! it says to cast on loosely 30 of one color and then 20 of another color. Then garter stitch for 60 inches. twist 2 yarns together when they meet on each row. I have tried this multiple times now and I keep getting a V look because the yarns don’t seem to be attached at the beginning and then it just looks bulky when they come together. Am I missing a step when it comes to the first row of kniting? or is it during the cast on process that I need to do something to keep them joined so there is a nice flow from one to the other? I’m using circular needles. Thanks for any help that is given. This is one of the free patterns given on this site - the red and orange pullover if that helps. Sure looks simple - but I am not so sure now!!

There’s a ‘How to knit with 2 colors at a time’ section under Advanced Knitting. Check out ‘Intarsia.’

Additional info here. There are pics of what the back/front of your work should look like with the yarns properly wrapped.