Cabo is guerrilla rank 5 in Libertad. It unlocks a new tier of weapons and gear from Juan and his Arms Dealers, including the Gladiador Supremo.
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.
By Cabo you have access to a wide spread of Supremos. Check Juan's shop after you rank up, since several items only appear here.
Rank 7: Teniente
Libertad rank 7. Weapons and gear marked for Rank 7 can be bought from Juan and his Arms Dealers.
Rank 3: Exploradora
Libertad rank 3. Weapons and gear marked for Rank 3 can be bought from Juan and his Arms Dealers.
Zona Medicina
Releases a healing cloud that doubles health regeneration for you and nearby allies. With a full charge it can revive you.