Very likely you project websites occasionally to demonstrate things to the class or do screencasts of using the internet. Having small font can be a hinderance for students understanding clearly what you are doing.
Zooming into the webpage makes for clearer presentations and also screencasts.
Note: If you are on a PC you use the CONTROL key instead of the command key.
To zoom in on a webpage hold down the command key and press the plus key repeatedly. Not only will I use this when presenting but also for screenshots so that my icons are larger.
Once you have zoomed in you will probably want to zoom out. Hold down the command key and press the minus key repeatedly to zoom out. I will also zoom way way way out on graphics I am making so I can take a screenshot of the graphic and have a thumbnail.
Of course you want to put the zoom back to normal. Hold down the command button and press the zero key once. If your website is looking a little weird, you may have accidentally zoomed in on the page. Try command zero to see if that does not fix things.