Hola James

Haber is an auxiliary verb that is in lots of lessons, especially in those that test on conjugation of perfect tenses. If you go to Library, you can search there, include the word "haber" and you can also try by typing "El pretérito Perfecto" or "El pretérito Perfecto Compuesto". Haber is also used in an impersonal way to say "there is, there are, there was..." so type these words in the search. The lessons will come up. 

If you can't find them, let me know and I can redirect you to specific lessons, depending on your level.

Saludos

Inma