How do you add different colors?
Generally just start knitting with the new color. If there is a hole where you started you can fix that later with the tail.
What are you making though? Is it just stripes or are you doing some sort of pattern? Including a link is a good idea when asking questions so we can be sure to give you the correct answer.
I am trying to knit the heel of a sock. I don’t have a link, sorry. I got this pattern out of a book. Thanks!