Feed the starter every time you use it. When you take some out, just put some flour and water back in, or you can feed it some dough or batter from the recipe you are making. If you haven't used it for a few days, just stir in a little flour. You don't have to remove any, unless you have too much and it's bubbling over. It can be composted.
If you have an earthenware crock, use that to store it. It should be kept covered with a lid or cloth (not airtight though). The next best thing would be a glass jar (wide mouth) or bowl. It can be kept on the counter if you use it every few days. If you're not using it that often, store it in the fridge. If you won't be using it for a couple weeks, it can be frozen, though I've never done this.
It can be used different ways, but here's my method for bread: The day or night before baking, feed the starter so that you will have enough for a couple of cups plus a little left over. The next day, take a couple cups of starter and combine with the flour, water, sweetener, and additional yeast (if using) from your bread recipe. This is your sponge. It should sit for at least an hour, but can be left for a day or so, depending on your preference. Fold in salt, oil, and knead in remaining flour, then let it rise again once or twice. Shape into loaves, and bake when risen. For quick breads like pancakes or waffles, I don't usually leave them to rise. I just add some baking powder. You will still get the nice flavor and nutritional benefits of the starter.
I usually have about 2-3 cups of starter going. If I need more for a big batch of bread, I will just feed it a day in advance. I usually try to leave about half a cup to get more going, so once I have taken from it, I stir in 1-2 c. fresh flour and enough water to make a thin batter. Sometimes I add a little honey or maple syrup. You can use it as soon as the next day. There are no hard and fast rules really, just feed it here and there, and use it often- I've heard it said that the more you use your starter, the better it gets.
Hope this helps.