If you are using the Google Chrome browser and want to zoom in on the screen (particularly useful if you are in a Google Hangout and want to screenshare) you can go to the 3 stacked lines in the upper right hand corner of your browser.  This is where you can find your browser settings.

One of the settings is zoom.

If you have zoomed in or out (on purpose or not, sometimes using a trackpad you can accidentally pinch zoom) you can return to normal by holding down the command key on the Mac (control on PC) and hitting the zero key.