Let’s say it’s 12th century England or France to narrow the question. How do I, as a non noble, become a professional soldier and not tied to the land? How do I join a retinue and become a paid member of an aristocrats circle or soldiers?
The idea of conscripted peasantry is one of those popular misconceptions that just keeps surviving (Thanks GRRM.).
HERE is /u/DanKensington's thorough literature review of posts from this sub about how armies were raised and equipped throughout the Medieval period, and how you might join up.
I discussed earlier how one of the rare sytems of peasant "conscription", the Early Medieval English Fyrd, was recruited here.