All in all, definitely not a hard recipe to make. I know most people understand the basic ideas behind this- and every recipe is different! I also must apologize for the fact that when I go rogue from recipes to try to make my own stuff up, I too frequently don't keep track of the amounts I'm putting in- so I'll try to make a better effort with that in the future!
I always start by taking whatever amount of potatoes I want to use (generally 1 potato or a little less per person is a good rule of thumb), and washing them off, then peeling about 2/3 of them, leaving some parts of the skins on. Cut these up into pieces (smaller will boil faster) and throw them in a pot of water that just covers the potatoes with a little bit of salt. Turn on high and let it boil, then leave the potatoes in the boiling water until tender (when a fork can easily cut through them). Leaving them in longer will make them easier to mash!
While the potatoes boiling, I put butter (stick form), heavy cream, parsley, and minced garlic in a bowl to microwave for about a minute in inrements of 30 seconds to melt the butter and warm up the cream. Heavy cream serves the same purpose and milk and can be used instead, but is a little thicker and creamier. The amount of these vary depending on how many potatoes you use... but it's better to start with less and add more once the potatoes are in if you need it so as to not make them too runny. You can buy minced garlic in jars from most grocery stores. We personally have the economy sized jar and still go through it like wildfire!
Once the potatoes are boiled and drained, place them into the bowl with the melted butter and cream. We use a potato masher, but you can also use a hand mixed to make them more smooth or even just a spoon for a chunkier mash. Salt and pepper to taste, and add more heavy cream or butter a little at a time if necessary. In this batch I also threw in a little bit of shredded mozarella cheese. Sharp cheddar also works wonderfully if you've got it laying around. Voila!!!