I think the term 'lay Buddhist' might fit more appropriately rather than using 'secular' as a descriptive adjective.
A person who hears/reads the Buddha's teaching, contemplates it, finds value in it, and wants to use it as a basis for waking up from the dreams of delusion of this fleeting existence, can decide to formally become a Buddhist. That entails finding a recognized and qualified teacher (most often in a Theravada, Zen, or Vajrayana tradition) and, with sincerity in one's heart, taking refuge in the Buddha (the teacher), the Dharma (the path), and the Sangha (those companions established on the path).
Becoming a Buddhist comes from an inner conviction that by applying the Buddha's teaching, through one's own efforts and discernment, one will eventually lessen greed, anger, fundamental ignorance, and so on. At the same time, one will find that positive qualities such as the wish to benefit oneself and others in a non-dualistic way increases.
There are many ways to go about Buddhist practice. They all boil down to using the methods that countless practioners have found invaluable over many centuries.
I hope my meager understanding doesn't confuse the issue.