Oops, forgot to mention you do need a bottle of Ammonia as Diaze has said.
You can get ammonia from Homebase, although not all Homebase stores have these, its an own brand Household Cleaner Ammonia, with 9.5% Ammonium Hydroxide which should be fine to use
(a tip, shake the bottle, if ammonia froths at surface and does not dissipate quickly, not good, if just a few bubbles that dissipates quickly, then thats fine)
Online, you can purchase Kleenoff which seems a fairly popular brand on this forum for tank cycling.
Or you can go online to eBay and get Aquarium Ammonia which should give several choices.
Also purchasing small syringes or droppers will be of benefit when it comes to adding ammonia dosages to your tank.
To calculate ammonia dosages, just use the forum calculator (you'll find at top of forum page almost in middle)
At bottom of calculator page, you should find Fishless Cycling - Ammonia Required.
Input your tank volume, then change desired level of ammonia from 5ppm to 3ppm then you'll get your dosage calculated as Solution required in ml.