Machetera is the first guerrilla rank in Libertad, where every new recruit starts. Ranking up from here opens new weapons and gear at Juan's Arms Dealers.
Your guerrilla rank rises as you earn XP across Yara. Each new rank opens a new batch of weapons and gear for purchase, and some items say right in their unlock text which rank you need. The game shows either the feminine or masculine form of each title.
Follow the story operations and pick up nearby Yaran Stories and FND checkpoints. Early XP comes fast, so you will leave this rank quickly.