If you don't feed the bacteria (e.g. putting ammonia in your tank and alittle fishfood), fishless cycling is useless.
If you keep fish in your tank (DON'T PUT AMMONIA THEN), bacteria get food and increase but fish will suffer ammonia and then nitrite until there is enough good bacteria to oxidize NH3 -> NO3-. And when you put more fish in your tank, ammonia/nitrite spike come again because there isn't enough good bacteria to treat increasing "products" of new fishes' metabolism.
When you feed bacteria (fishless cycling) and testing water values you see first that NH3/NH4+ is increasing.. After one/two week/s NH3/NH4+ start decreasing and NO2- start increasing (nitrite spike), then after week/s nitrite start decreasing and NO3- start increasing. And when you put more ammonia on in your tank, NH3/NO2- won't increase but NO3- will increase if you check water values aften couple hours. Then your tank is ready for fishes.
However, remember to make couple huge water changes before you put any fish in your tank and check NH3/NO2-/NO3- levels.
NH3 should be 0 mg/l
NO2- should be 0 mg/l too
NO3- should be 2-10 mg/l (not zero, because it's important to plants)