Yes you can fly through clouds but you would need an instrument rating. A private pilot can add an instrument rating to their certificate which requires a minimum of 40 hours of instrument training and simulated instrument flight time.
To fly within the continental United States you do not need a FCC Radio Operators Permit, however if you plan on flying internationally a permit is required per ICAO (International Civil Aviation Organization) regulations.
A debrief is something that you would do after a flight to review identify anything that can be changed or done differently. In a flight training context it typically is done between a flight instructor and a student after a flight to identify events in the flight that could use improvement or things that were done well. It is used as a tool in the flight training process.
You mainly learn how to talk on the radio through practice and experience, however there are other things that you can do improve your radio proficiency. Many people listen to websites that play live radio channels so they can pick up on terminology and practice listening to ATC, a popular website is www.liveatc.net. There are also courses you can take to help such as Sporty's Pilot Shop VFR Communications Training. https://www.liveatc.net/ https://www.sportys.com/pilotshop/sporty-s-vfr-communications-online-course.html
A TFR is a Temporary Flight Restriction and is an area of airspace that the FAA can designate as restricted. The FAA defines TFRs as "an area restricted to air travel due to a hazardous condition, a special event, or a general warning for the entire FAA airspace." A common TFR is for when the President or Vice President are in areas outside of the Washington D.C. When the President travels around the country there is a 30 nautical mile TFR around him at each location. The Vice President typically has a 3 nautical mile TFR. Another example of how the FAA uses TFRs is in airspace around fires to protect the fire fighting aircraft working to put out the fire.
Disclaimer: Advice received via the Pilot Information Center and AOPA websites should not be relied upon for personal, medical, legal, or financial decisions and you should consult an appropriate professional for specific advice tailored to your situation.