"Pass me that bottle of ketchup."
"Can you pass me that bottle of ketchup?"
Both sentences are similar and different in their own ways.
Similar in the sense that they convey the same message. Different because the former is called commanding and the latter, requesting.
Command is harsh. A request is gentle and respectful.
People respond to command and request differently. Commanding works well when someone is under an obligation to do something, like in an army. For other cases, requesting works better.
You see, you can't just treat people as your slaves. If you want someone to do something for you, it's better to gently ask him/her to do it instead of commanding. The former will get you better results.
Ask, don't command.