Reading yarn size or weight

[Riany]

I received to HUGE balls of Bernat cotton yarn for my birthday!! whoohoo

But I don't know what the weight is?! On the upper left hand there are a couple of pictures the first one being Medium (4) would that be yarn ply? I kinda understand looking for patterns using ply and weight.

I haven't been able to do any projects since my fingerless glove, so this was a defenate bonus!