PLEASE take a minute to search the forum, read the FAQs, etc.
Frequencies used are usually FRS+GMRS (UHF band).
Sometimes (often? usually?) frequencies are assigned to teams/sides. And as for "running any frequency you want" that would still be limited to the FRS and GMRS frequencies: there are [licensed] people using other frequencies out in the real world, you can't just start broadcasting all over the place -- they will
be upset and if you get caught you will
get in trouble. Radios are not toys.