How to properly use seafoam

[NVA-AV6]

it actually says on the back of the can not to use it in high milage cars because it will clean the engine so good.  And on higher milage cars theres carbon thats filling in leaks and helps seal areas that are worn out, so cleaning that will cause leaks.  Dont know its true but a possibility

That is partially true, the whole story is that that carbon that will be losened up will scratch and scar your cylinder walls and clog your cat(s).

[Sworkhard]

so from what im reading your not supposed to do it directly into the engine, you put it into the gas tank and let it run out before doing an oil change?

You can use seafoam in 3 different ways.  Either through the intake, in the oil to clean up sludge, and in the gas tank to clean the injectors.