Does pushing Ctrl and + at the same time help? You can do this multiple times to get the size you want.
I don't know about other browsers, but in Chrome there will be a little magnifying glass at the right end of the bar where you type the website address (just to the left of the star) if you you are zoomed in or out. You can click the magnifying glass, it wall pop up a little box, and you can click the button that says "Reset". That will get you back to default zoom.
First time Chihuahua owner with many years of dog experience!