how do i check them if i have a leak or not?

my rpms are real low and i've narrowed it down to being a leak in the VLs or the O2 sensor... i just dont know how to go about checking the vaccum lines or even where to find them. i know i know i sound like an idiot but i cant help it, i bought a honda for my first car i mean that explains everything right there

 

I only know there is one vaccum line connected to the break booster and there is a valve between the hoses. You can check it's condition by blowing into it with your mouth. not sure about other vaccum line.

 

there's one at the back of the engine near the firewall, right behind the farthest part of the valve cover, connected to the fuel pressure regulator (I believe)... or it might be part of the AIV

 

You check them with a vaccum gauge. There is charts (where i dont remember) on the different types of problems due to how erratic the needle on the gauge is.