What does it mean when you have a fee?

I'm curious, could you explain what exactly is meant by having a fee in the world of cryptocurrency and finance? Is it a standard practice across all transactions? How does it impact the overall experience for users and investors? Additionally, are there any specific fees that are more common than others, and what factors might influence their amount? Understanding the intricacies of fees in this field is crucial for making informed decisions, so I'm eager to gain a deeper understanding.