Here's a breakdown of the parts:
* fidem: This is the accusative case of "fides," which means "faith," "loyalty," or "trust."
* praesto: This is the present tense, first-person singular of the verb "praesto," which means "to offer," "to provide," or "to make available."
The phrase emphasizes a willingness to stand by one's commitments and demonstrate trustworthiness. It's often used in a context of making a promise or pledging allegiance.