The answer to your question depends on the version of the Mac operating system that you're using. If your Mac is just a few years old or newer, you would move your mouse pointer to the upper left-hand corner of the application window that you're working in, and click on the green button (the one furthest to the right.) That would put the app you're working in into fullscreen mode.
On an older Mac with an older version of the Mac operating system, you would move your mouse pointer to the lower-right hand corner of the application window you're working in. You'll see your pointer change into two arrows pointing away from each other. Click and drag the window border until the window covers your entire screen. There unfortunately is no 'maximize' or 'full-screen' button on older versions of Mac OS.
I hope this helps! If you have any questions, please let me know. Thanks!
