The nether reacter gives you a bunch of cool stuff including sometimes a gold bar or two!
Get 4 gold blocks and put them down like this, with a space in between each one.
Then, put cobblestone in between the gold.
Next, put the neather core on top of the middle block of cobblestone.
Next, put 4 blocks of cobblestone on top of the gold.
Next, place a cobblestone block on top of the nether reacter core. Then place 4 cobblestone blocks on the sides of that cobblestone block you just put down.
Finally, get close to the core and tap it with something made out of diamond, like a diamond pickaxe. (If you are playing on multiplayer all players will have to go close to it).
And bada-bing! It is active!
Now this is when it spits out stuff for you to collect!
When it is finished you will escape out of it with little holes that appear, when you leave it will be night. This is what it looks like when it is finised and you escaped.
These are some of the stuff it gives you!