Why am I being charged a brokerage fee?

Excuse me, but I was wondering if you could clarify something for me. I recently noticed that I was charged a brokerage fee on a transaction I made. Could you explain to me why that is? I understand that there may be some costs associated with executing trades, but I'm not entirely clear on what specific services the brokerage fee covers. Could you elaborate on the reasons behind the fee and how it's calculated? Additionally, are there any ways to potentially reduce or avoid this fee in the future?