A good system will come with instructions.
If you havn't bought the system yet, then you need to decide which type you want.
Plumbing side: You can get a vampire tap into the water and drain supplies, this is easy, but can never be removed without repairing the pipe. There are garden hose thread adapter, which is great if you want to install this in a laundry room where you already have a threaded tap available. There's a faucet diverter to hook up to a normal faucet, but I don't think that's very nice for a permanent hookup. For both the hose thread and faucet adapters, you can support the unit above sink level, and let the drain line run into the sink.
Output: If you want to use the RO
water for family drinking/cooking as well as the tank, invest in the pressure tank and faucet. You may have to drill a hole in your sink to mount it. If this is going to be used for fish only purposes, then consider a float valve and resivior, you'll get more water out of the float valve setup than the pressure tank.