Changing colors

I was looking at a different site and I saw that I can use duplicate stitch method of joining the yarn. (I want to set up to do intarsia) But it doesnt explain how to do it . Can anybody help?
Also, my pattern has a block of black and then the next row has one block over can I still use the same yarn or do I have to restrand?

We might be able to help you more if you provide a link or name of the pattern you are working on.

Amy does have a video of the duplicate join here:thumbsup:

ETA: Is this the Tigger Afghan?