When I was young and on a very small budget, I often when to the LFS to buy a test kit...
And always came back home with food or else, every time.
With a little common sense and discipline. Nobody really needs a test kit. We cycled numerous tanks without ever testing anything, nor adding any startup stuff. As young as we where and succeeding ... It's certainly not rocket surgery.
Your eyes are enough to see how thing are going in there. Maintaining it before it degrades is key.
But Once you can have a test kit, you will quickly understand, how the cycle works.
Just this graph is enough to catch the principle...
This is how a perfect fishless cycle looks like.
It's a 2 step process that will convert a very toxic compound to a another toxic product that builds slower then will convert this to an even slower building and less toxic product. That you have to dilute periodically to maintain at safe levels.
You can trace your tanks own graph going along with your testing results.
This example is based on a fishless cycle and will kill any fishes and plants present in the tank. Because every compound released will reach levels that are too high before being transformed.
The Fishmore method will use the same graph but will use water changes to keep every compound under stressful levels, This can vary (frequency and quantity) depending on the fishes size and numbers. And a lots patience. Once the ammonia spikes start dropping and nitrite levels are growing, big part of the job is done in both cases.