How would I know if it's clogged ?

 

Idle will not show much difference but you'll feel major loss in acceleration once you get going towards high rpm. Your temps will be hotter as well. Check under the car after the drive and you might see it glowing red.
More info on this site somewhere if you search.

 

Noticed if was glowing red when I drove just to the gas station and back but the car didnt accel right

 

There are "symptoms" but there is no way to really know without truly removing/inspecting the cat and doing a flow test (i.e. backpressure tests).

 

I had a plugged cat once.The car wouldn`t accelerate for anything & fell on its face when I got on it. I unbolted the cat and just let it hang ( yes, it was much louder than stock ) & took the car down the road. Wouldn`t ya` know, the car launched and ran like there was no tomorrow.

 

Indeed it was clogged so I just gutted it !