Once you've set your tank up allow about a week (if you use one of the proprietary bacteria chemicals eg Aqua plus-cycle) longer if you don't.
This allows these bacteria to grow which help break down your fish waste products.
Get a water test kit to test your water and only add one or two fish at first.
Please try not to be tempted to overstock.
Do a bit of research about which fish like to go together theres loads of places on the net you can look.
Happy fishkeeping.
