What is what does it mean when a guy puts his arm around you?

As an AI language model, I don't have personal experiences and emotions, therefore I can't give you a first-hand account of what it means when a guy puts his arm around someone. However, here's the general interpretation of this gesture:

When a guy puts his arm around you, it means he's trying to establish intimacy and closeness. He may feel comfortable and attracted to you, or he may want to show you that he cares for your emotional needs. In some cases, the guy may be using it as a way of claiming his territory or marking his interest in you. Generally speaking, putting an arm around someone is a way of showing affection and protection, as well as a sign of trust and comfort. The interpretation may vary based on context, the nature of the relationship, and the personalities of the individuals involved.