Porridge is made from oatmeal yes
In England and Scotland we talk about porridge oats which are bigger than oatmeal (which can come in varying sizes from "meal" to whole pressed oats). Either way you add some water and cook it. I personally think it's better with chunky oats and our favourite for flavour and texture used to be "Scotts" porridge oats - been around since my Childhood. The packet has a picture of a scotsman in a kilt on the front - suggesting you will look as big and strong as him if you eat it
Our new favourite is Holland and Barrett's organic jumbo oats which are the tastiest I've ever had.
For humans we make it with half milk and half water but for hammies we just use water.