How to save the size of a window??

I Just bought my new 15" macbook pro, my first mac, after being a pc user for 10 years!, and something that is kind of bothering me is that the windows never remain the size, when i resize one to fit all the text. It always goes back to a smaller window when I close, and re-open it. Anyone know how I can keep it the same size? Thanks
-Steven.

Hold down the option key while resizing the window.

In Finder, default window sizes can vary by folder. To change the default size, open the Finder to the default folder which first opens when you open the Finder (usually your user folder). Resize this folder using the option key, and close it. Clicking the Finder dock icon should now open to the new default size.

There are a couple other ways to access other folders in the Finder without it opening your user folder first (i.e. clicking the HD icon on the desktop). As you find these, you will need to resize them manually, but there are only a couple. And they will only need to be set once using this method.