I believe everybody uses it wrong though. Technically "Amerika" is the continent. But most people mean "Die Vereinigten Staaten von Amerika" (The United States of America aka USA)
Depends on the context. If it is written/talked about in a geographic context, it will usually mean "the Americas". If it's in a political context, it will mean "the USA".
Keep on mind that reputable news outlets won't use "Amerika" when referring to the US however, they will use "Vereinigte Staaten" (United States). "Amerika" as a term for the US is very much a colloquial thing.
Depends on the context. If it is written/talked about in a geographic context, it will usually mean “the Americas”. If it’s in a political context, it will mean “the USA”.
The US. We'd usually use North/South/Central/Latin America for specifics, or if we wanted to imply something happens all over the Americas, then we'd refer to "the entire American continent" or continental America.