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Hola Sylvie

Gustar is a verb that used indirect object pronouns to indicate the person who is doing the liking. 

Indirect object pronouns are these: me, te, le, nos, os, les

• me = to me
• te = to you
• le = to him/to her
• nos = to us
• os = to you (plural)
• les = to them 

So, in this sentence for example:

This "le" is indicating that chocolate is pleasing "to her".

Here is a more basic lesson on gustar.

Saludos

Inma