Every two weeks is nowhere near enough--fish constantly excrete ammonia through their gills. Kind of like their version of urine. In nature, ammonia is consumed by beneficial bacteria and broken down into less toxic compounds and is consumed by plants and diluted by much larger quantities of water. However, in a small bowl you have to perform those functions instead.
Ammonia is highly toxic--it can lead to several health problems as well as death--and believe me, ammonia poisoning is a terrible way to die. Ammonia can burn the fish's gills and cause them to shed their slime coats, which is very torturous to them. Your friend sounds like a nice person to give you all that stuff for your fish--but they don't know how to properly take care of them.
You should take the time to do research for yourself and read this care sheet: http://www.bettafish.com/showthread.php?t=49160