Left to the graph you will find the caption "link to this graph". By clicking on the link you will see the link to your graph in a text box. You can send this link to a friend, share it or bookmark it. When entering this link you will see the graph which is currently in view. Click on the icon right to the text box to test your link.
You can add the x axis range or y axis range or both of the current view to your link by checking the boxes bellow the link.
For example, the link in the textbox in the screenshot in the right is: http://www.onlinefunctiongrapher.com/?f=cos(x)|sin(x)|tan(x).