The expression haber de followed by an infinitive verb usually means "to have to," "to be necessary," or "to be supposed to." This phrase is similar to tener que or haber que, but it expresses a much weaker and often vague sense of obligation. Haber de can and is used in normal speech, but is more likely found in literature and song lyrics.
In her new video, Raquel uses haber de to explain how to open a bank account:
Siempre hemos de asistir personalmente a la entidad bancaria.
We should always go personally to the banking entity.
Caption 9, Raquel - Abrir una cuenta bancaria
You can also find the expression in Muñeca Brava's musical theme, sung by Natalia Oreiro:
Que la suerte sea suerte y no algo que no he de alcanzar
So that luck becomes luck and not something that I can't reach
Caption 4, Muñeca Brava - 1 Piloto - Part 2
Also, in our Mexican movie, El Ausente we hear Valente Rojas daringly say:
En un minuto nací y en menos he de morir.
In one minute I was born and in less [than that] I shall die.
Caption 4, El Ausente - Acto 4 - Part 2
Since haber de expresses a milder sense of obligation or necessity, it's perfect to make a polite recommendation; it's less imposing than tener que or haber que:
Lo primero que has de hacer al reservar en un restaurante es...
The first thing that you have to do upon reserving at a restaurant is...
Caption 6, Raquel - Reserva de Restaurante
In the previous example, Raquel could have also said: Lo primero que tienes de haceror Lo primero que hay que hacer (Remember that haber que is only used with the impersonal form of the verb haber: hay (present) or hubo (past).) Haber de is simply more polite, even poetic.
Finally, you should know that haber de is sometimes used to express possibility, for example to make a supposition:
Ha de ser rica porque llegó en limosina.
She must be rich since she arrived in a limousine.
Ha de haber sido un intento de mi parte por conceptualizar a la sociedad norteamericana.
It must have been an attempt on my part to conceptualize American society.
Caption 17, Arturo Vega - Entrevista - Part 4
¡Deben de haber aprendido mucho con esta lección! Thanks for reading!