Rust In Camry

[KENN]

Hi everyone,
I am a new member to this forum but i have been visiting this forum for a while.
I have a Camry and there seems to be rust in the metal surface under the body(i am not very good at the parts but i think its the metal in between the axle).So i went to canadian tire and bought a rust check and rustconverter combo.I just want some input from anyone who has used it.Is it good or should i just leave the rust alone.
Secondly,it says it converts rust to a paintable primer.Is it necessary to paint it or can i leave it without painting.
Thanking u all in anticipation.
Regards,
KEN