Ana, Here in the USA, the common phrase would be "to cross your arms". Although both phrases really mean the same thing, the same action, you would almost never hear the phrase "fold your arms" here. As the others said, some people have the manner or habit of "crossing their arms" when they talk. Other times it can indicate a displeasure or a stern, strict, position of authority, for example: "The teacher looked at me, with her arms crossed, and told me that she was not happy with my behavior in her class!" I hope that this helps, feel free to ask for clarifications.

"Cross your arms" is the most commmonly used expression. I crossed my arms. She stood there with crossed arms. Some people cross their arms while talking. Hope this helps.

Yes, thank you very much!

Depends on the context. Both expressions are often used frequently, but folded arms is mostly used when you wrap your arms just under your chest, not necessarily crossing your arms, for example mummies have their arms crossed, but not folded. Some people also refer to the type of posture whether it is relaxed or defiant. The semantics depend on the context. I hope I've helped.