Do you mean the Dock (where your apps site) usually on the bottom? Or the System Menu bar along the top with the Apple logo, Menu titles and clock etc?
If you want a window to go past the Dock, then you can either 'hide' the Dock so you can get the window to the bottom of the screen, or move the Dock to the side.
You can't get your window to go over the System Menu bar.
Don't worry about trying to get them wide enough to fill the screen - it's generally a waste of time unless you really need the space when working on images etc. I've found myself keeping windows fully vertical (but narrow) even on my Windows PC at work lately - makes it much easier to flip between them or drag and drop.