Answer:
a weaved valley: you run one shingle at least 6inches past the valley onto the opposite side of the valley from each side all the way up
alternating them each time so they overlap like a weave on top of each other This does not work well in pitches are different and often look sloppy. keep in mind that the top of the shingle has to be 6 inches past the valley center. Another thing to keep in mind is to be really careful of your nail pattern, do not nail in the valley keep nails above the rain channels skip a nail if too close (6" away at least)
I like a clean cut valley, to do this run the shorter rafter section first, unless you are running a flatter section like a porch then run the flatter section first. you will run all the way up on the first side lapping a min of 6 inches past the center of the valley at the top of the shingle. Keep nails away from valley center by about 6" or more, and make sure to keep nails above rain channels only, skipping if necessary. Keep in mind you do not want a seam too close to a valley. Now you run the other side running till the top of the shingle is just short of the center line of the valley. Take a chalk line and pop a line 1 inch short of the center of the valley, cut with a hook blade being careful not to score through the shingles below.also when there are two different pitches the flatter of them will require one or more added to keep center of vally