You can change the viewing window to better fit the data you're looking at. For making easy adjustments while accessing Desmos in the browser, you can use the plus and minus signs to zoom in and out, respectively, on the coordinate plane. You can also use the house icon to go back to the default viewing window which is pre-defined depending on the screen size.
To zoom in and out on mobile devices, you can pinch the screen. It's also possible, only on mobile, to zoom in and out on a single axes by touching two fingers to the axis and pinching.
For more extensive data, you may find it easier to manually adjust the domain and range of the viewport. To do so, click on the wrench to open the Graph Settings menu and choose which axis you'd like to adjust.