Vigenère Cipher
The Vigenère Cipher is a version of a Caesar Cipher, where each letter is shifted based upon a keyword.
In the applet, S is the 19th letter, so the first G in GeoGebra is shifted by 19 to Z.
T is the 20th letter, so the E in GeoGebra is shifted by 20 to Y.
The letters include the "&" to be used as a space.
Use a reasonable key length.