I used a product called "nutrafin cycle" it markets itself as a biological aquarium supplement. There are many on this forum who doubt they provide anything beneficial or actually work. As i mentioned before only been involved in the hobby for a very limited time, so my knowledge is only limited. Will offer my own advice based on personal experience if you wish.
What i would advise as your first step is either buying a water testing kit, or if it's close and convenient, some Local Fish Shops may do them for you. Be a good idea to find out your tap water levels initially, heard advice to let the water sit for 12 hrs before testing.
Some stuff in your tank may affect water readings - type of substrate used (sand/gravel/etc) pieces of wood, type of stone.
OR... Another Option
would be a "Fish-Less" cycle, many on this forum would be able to offer advice on this. There are many pages of good advice on this forum.