Photoshop newbie,layer mask problem

I am a total newbie to the world of photoshop,pretty much only ever use it to clone and heal.I know i have to learn layers and masks,so i thought today i would give it a go,and already have a massive headache.

I have opened an image (one above) made a layer mask,and started to paint out the cushion,when i do,instead of the cushion disappearing (like i see in some tutorials) all i get is this white and grey chequered effect,and when i click back onto the image,it is still there.Now call me stupid if you like but i am buggered if i can see what i am doing wrong?

I have also tried making a duplicate layer,and then adding a mask,but nothing.I have absolutely no idea what i am doing wrong.I realise this is probably the most basic thing in photoshop but i am stumped.

I am using photoshop CC 2015

Any help greatly recieved