Quiero, quisiera, necesito

Quiero

With quiero we can simply use the name of whatever item it is that we want, as in the following examples;

Quiero un café.             I want a coffee.

Quiero este libro.           I want this book.

Quiero dos entradas.      I want two tickets.

however, we might need to say that you want to do something or be something, as in these examples;

Quiero tomar un aperitivo.       I want to have an aperitif

Quiero hablar español.            I want to speak Spanish.

Hoy quiero estar en casa.       Today I want to be at home.

The verb that follows quiero in each of these sentences is in the infinitive form.

Quiero Can be used withe reference to a person(though you also have to insert the little word a before the name), but in this context it means I love... . For example:

Quiero mucho a mis padres.             I love my parents very much.

La Sra. Méndez Quiere a su marido.   Mrs. Méndez loves her husband.

Quisiera

In English there is a difference in tone between the straightforward I want and I would like, which is less blunt and demanding. A simmilar difference exists in spanish between Quiero and Quisiera.

Quiero un Café.                         I want a coffee

Quisiera un café                        I would ke a coffee.

Quisiera hablar bien el español.    I would ke to speak Spanish well.

However, quiero is quite acceptable in most circumstances, for example when ordering in a restaurant.

Not that quisiera ends in -a whether it is used withe I or he/she/it/you.

Necesito

Necesito works in the same way as quiero in that it can be used with a noun (the name of something or someone) or with the infinitive form of a verb.

Necesito un billete de ida y vuelta.    I need a return ticket.

¿Necesita Vd. viajar a Zaragoza?      Do you need to travel to Zaragoza?

Necesitan un coche.                      They need a car.