How does a fixed charge work?

Excuse me, could you please elaborate on how a fixed charge functions in the context of financial transactions or specifically in the realm of cryptocurrency? I'm curious to understand the mechanics behind it, particularly how it differs from other types of charges that might be encountered. Is it a predetermined fee that remains constant regardless of the transaction's value or size? And if so, how does it impact the overall cost efficiency of the transaction? I'd appreciate any insights you could provide to clear up any confusion I may have.