How do you shear a sheep on Minecraft Pocket Edition?

Two diagonal iron ingots.
Shears are made by placing two (I)ron Ingots in your own crafting slots in the following configuration, where E is an empty space.

EI

IE

It can be done at a crafting table too of course.
Place two (I)ron Ingots in the following configuration,

EEE

EIE

IEE

Where E is an empty space.
In your 2x2 or 3x3 crafting grid, 2x2 as shown below:

1 2

3 4

Place an iron ingot each into positions 2 and 3 and this will create 1 pair of shears.