Agencies 1-Reference Wikipedia too

I'll do this in stages because it's long.
The CIA, aka the Company and the Agency is utilized the US for non-domestic intelligence. By that I mean they have no jurisdiction in the US. That is the role of the FBI. However, on occassion, they will observe domestically. There are many groups within the CIA. The Clandestine component being the most familiar. However, they have a special group, SOG, that operates as a paramilitary group. They will bring others in fromthe Navy Seals, Delta Force and Special Operations in general. This is called Sheep Dipping. Training is done at the Farm near Williamsburg, VA.
The CIA operatives rarely do the spying themselves. They engender others, called assets, who have access to desired information to actually to the covert work.
The CIA operatives have to figure out who will be a reliable asset, give them missions, put together and analyze the information.
An asset can turn out to be a double-agent and the officer will need to be extracted.
Official cover operatives are granted a set of governmental protections,and if caught in the act of espionage, they can request diplomatic protection from their government. This is very common.
There are also operatives, who have Non Official Cover, who assume positions with no ties to their government, and whose actions are officially disavowed by that government.