Can someone explain what is meant by the paragraph below in regards to symbols?

I can’t understand the difference between symbols and strings in ruby still… Could anyone explain the paragraph below, maybe use a simple example? This my first time on a back end language.

Strings can be changed, so every time a string is used, Ruby has to store it in memory even if an existing string with the same value already exists. Symbols, on the other hand, are stored in memory only once, making them faster in certain situations.