Ok, now, there are millions of threads on this forum with detailed infomation and you should have a beginners book with establishing a new tank info in it. That said, cycling is the process your tank goes through to make it ready to house live critters.
It takes a period of time for beneficial bacteria to build up in your tank that will adequately break down ammonia produced by the inhabitants of your tank into a relatively harmless byproduct, nitrate, which then is removed during routine water changes.
How do you do this? Simple. SEt your tank up the way you want it. Get the temp and salinity where they should be. Make sure you have test kits for ammonia, Nitrite and Nitrate (minimal)
Turn on your filters, pumps etc. Then add a smelly old pice of shrimp to the tank.
Get a notebook to keep track of the changes your tank will go through.
First you will see ammonia spikes, then die down to be replaced by high nitrite readings. then fnially you will see the nitrites disapear and have measurable nitrates.
Do NOT add any live critters to your tank if you have any ammonia or nitrite.
Once your tank has gone through this first cycle, do a partial water change-10-20%
Check al your water parameters again, then and only then you can add your first fish, or if your tank is large enough, perhaps two small hardy fish.
You can also cycle with uncured live rock, which is what I do.
Does this help?