Set up
You may download Geogebra from its official homepage or use the WebStart provided there.
When you access a Geogebra applet with a browser, you may double click inside the applet area to find out whether the file can be edited online, in which case a new window will be opened.

The interface can be switched from English to Chinese. [Options > Language > Chinese]

The font size can be increased, particularly when displaying the files for whole class teaching. [Option > Font size]

When you are working mainly on geometrical constructions, you may hide the axes and close the algebra window. [View > Axes ; Algebra window]

When you are working mainly on graphing of functions, you may set up an appropriate grid and use the input field at the bottom of the window for entering expressions.

Files created with Geogebra has an extension ".ggb". A Geogebra file can be exported as an applet in an html file. [File > Export > Dynamic Worksheet as Webpage]