The green button on top of my safari browser doesnt always do the same operation. Sometimes the window maximizes to fill the screen and sometimes it just doubles in size. How do I maximize the window to fill the screen everytime?
OS X doesn't work that way. The green button is designed to expand the window to the best size to fit the content, it isn't an actual maximise button. It's not really designed to have things fullscreen like with Windows. If you really want your browser to take up the screen, you'll have to drag from the bottom right-hand corner to expand it yourself (and will have to set the dock to automatically hide).
Easiest way: Just make any bookmark, by dragging the favicon (the icon by the address) from any page down into the bookmarks bar and edit the name and address, by right-clicking the new bookmark.
...or you could Show All Bookmarks, and make a new bookmark in the Bookmarks Bar through that...