The structure をください is used to politely request or ask for something. It literally means "please give me ~" and is one of the most fundamental expressions for making requests in Japanese. It combines the object-marking particle を with ください (the polite imperative form of くれる, meaning "to give").
The most common use is when asking for a physical item, such as when ordering at a restaurant or shopping.
You can specify how many of something you want by adding a counter before ください.
When pointing at something, you can use demonstrative pronouns with をください.
In more formal or polite situations, おねがいしますお願いします can replace ください for an even softer request.
をください is used specifically for requesting objects or things. To ask someone to do an action, use the て-form + ください (〜~てください) instead.