Adding new thread

I am knitting a dog sweater and are now at the leg openings where it says to attach a new ball of yarn to each section which will be two, between the legs and beyond the second leg opening. How do you attach the yarn to a loop?

Generally when you add a new skein of yarn you just start knitting with it and weave the end in later. If there is still a yarn attached you, like where you cut it, you can tie it loosely to that and then start knitting. At the end you can untie the knot and weave in the ends or just weave them in as they are.