Double knitting confusion

Ok I get the whole idea about how to knitt so both sides are different but I don’t get how to cast on so I get the stitches I knit with. Help…anyone. :oops:

Either cast on half the required sts with both colors held together as one and switch them around as you knit the first row so that they are alternating. This will give you a “mottled” looking CO edge

OR

Cast on using one color and add the second color on every other st in the first row…

omg thank you lol it worked perfectly…ok no wait lol I just checked it there’s a problem…probably something I’m just forgetting to do. On one side both colors aren’t attaching. SO you can see between them at the end of the work. What can I do?