The use of 'tú, vosotros' versus ' usted, ustedes' changes a lot depending on the Spanish speaking country or even the region. In Latin America and a few parts of Spain, they do not use 'vosotros sois' (or any other form of the second person plural of verb tenses). They use 'ustedes son' for both the formal and informal ways of addressing people. This might fit a bit with what your book says but only partly as the second person singular form of verb tenses ('tú eres') is universally used in Spanish speking countries.

A little piece of advice: check where your book was published and make sure it is still good enough. Things have changed dramatically since 1939 in what regards both language use and language teaching methodology. After some research on available books and resources, you may feel like considereing a more modern approach for your self learning.

Usando en la mayoria de las ocasiones tu y vosotros acertarás más de un 90% de las veces, solamente usted y ustedes en situaciones formales: con personas mayores y desconocidas, con superiores en el trabajo, ante agentes de la autoridad, ...

Incluso en regiones o paises donde el usted/es es más usado te entenderán.

Pero en definitiva la práctica y no la teoria es la que más ayuda oir conversaciones en tv e internet por ejemplo y aprender cuantos más ejemplos mejor. La teoria es una forma de apoyar y aposentar mejor la práctica y no al revés, así es como aprendimos de pequeños, de lo particular a lo general.

In brief:

First the examples later abstraction (magicaly, the mind by itself will do abstraction).

from the particular to the general.

I'm from Spain and I only use "ustedes" in a very polite situation. Nowadays in Spain we often use "vosotros" and we only say "ustedes" when it's a very polite situation. (if you are able to listen to a radio program or a tv serie from Spain and from Latinoamerica you will see the difference)

If you are plannning on going to mainland Spain, I suggest that you learn the vosotros form. When I started to learn Spanish I did not bother to learn verbs using vosotros, now I find it hard when I hear a verb spoken to me in the form of vosotros.

I have tried to learn it latley but, in my head I have the ustedes ready to use without thinking, but if I want to use vosotros it is really hard, I have to think about the construction first rather than just speak.

As Marta said, check another books and resources because that kind of books sometimes are not that helpful and they could be even confusing for foreigners.

Let's begin with (Tú vs usted). As she said ('Tú eres') it is used in every single spanish speaking country. (Usted) it is used to show respect or admiration for someone who, in most cases, is older than you. For instance if you visit your girlfriend's father or grandfather for the first time you will refer to him using (usted) but if you meet her brother probably you'll use (Tú).

And then (Vosotros vs Ustedes). ('Vosotros') is mainly used only in certain regions of Spain such as Madrid. But what you have to take into account is that anyone will understand you perfectly whether you say ('vosotros') or ('Ustedes') because both mean exactly the same, the only difference is that ('Ustedes') shows respect as ('Usted') but what we are are trying to say is that in many countries from South America or even in Canary Islands (where I am from) we use (ustedes in the place of vosotros) and it has almost lost it respect connotation because we use it all the time. If I were you I would always use ('Ustedes') because everyone will understand you anyway.