It's not like your iPad because it's not an iPad. Also, you don't have a refurbished Mac, you have a used one, and it looks like you're running a fairly old version of OS X.
If you want the app to run full screen, drag the corners of the window to make it full screen. Newer versions of OS X actually have a "full screen" button, but I never understood why anyone wanted a window to fill the screen if all the information could be displayed in a smaller window.