In basic terms, the acoustics of a room determine the quality of sound waves. Are carpeted room will sound different than one with hardwood floors, for example. When it comes to recording studios, room acoustics affect not only the quality of recorded instruments and voices but the speakers that playback those instruments and voices.
The importance of room acoustics cannot be understated.
I made this video awhile back:
Foam worked at “Studio B” decently well but if I could do it all over again I would use Fiberglass panels. Reason being is foam doesn’t cut low frequencies as ineffectively, which results in a “muddy” type of room sound.
Many do-it-yourselfer types swear by Owens Corning 703 framed inside of acoustically transparent material. But acoustics are a topic unto their own and rehashing material on DGTRS makes no sense. The sites mentioned above will get you started on the right path to not only what panels to use but how to construct/modify your studio as well.