A nether reactor is a structure that is made when you detonate the core. When you first detonate it there will be a whole bunch of stuff spawning around you. For more information go here: http://minecraft.gamepedia.com/Nether_Reactor
Step 1: Find a Clear Space.
This was also all done on pocket edition.
Step 2: Mark Your Base
You Will Need
1 Neater core
4 Gold Blocks and
Step 3: Make Your Second Layer
Step 4: Make Your Third Layer
Make sure you've made the right pattern or the nether reactor wont work.
Step 5: Hit the Nether Reactor With a Sword
Kill all the zombies!!!
Step 6: Collect All the Loot!
Congratulations you've made your First nether Reactor. I hoped you liked this tutorial and please vote.