European Spanish (Peninsular Spanish)
Generally speaking, we refer to Castilian Spanish, castellano, to talk about the national language spoken in Spain, which originated in the region of Castile (Castilla). But bear in mind that this is synonymous with español, which is the official language throughout the country.
In the Spanish peninsula there are variations of spoken Spanish. Depending on the area or region, the phonetic will change, there will be a different accent and sometimes slightly different grammar rules.
For example, in the southern region of Andalucía, the Spanish spoken by its inhabitants has a very distinctive accent. Although it varies depending on the city, town or village in question, there is a general use of the -s- sound in words that are written with a -c- or a -z-. There is also a general omission of the -s- sound at the end of a word, therefore plural words sound as if they were singular, for example, "cuatro gatos" sounds like "cuatro gato".
In central and northern areas, such as Madrid, Salamanca, Barcelona, Zaragoza, for example, the accent is more standardised and, unlike Andalucía, for example, all -z- and soft -c- sounds are heard as their original sound, which is the equivalent of the unvoiced "th" as in "thing" in English.
In peninsular Spanish there is a general use of the pronoun usted/ustedes as a formal you, instead of the informal "tú/vosotros".
The formal pronouns usted/ustedes are used in certain situations, mainly when there is a formal/serious interaction with the other speaker; for example, in an interview, with a client, or doing business. It is also common to hear usted/ustedes as a form of respect when talking to elderly people. In certain areas of Spain, it is even used to talk to older relatives, even though they are family and well known to the speaker.
However, outside these contexts, the most commonly used pronoun to refer to "you plural" is vosotros. This differs from the common use of pronouns in Latin America.
Note that with Progress with Lawless Spanish you can choose if you study peninsular Spanish, with testing on the vosotros form, or Latin American Spanish. Read more here: What kind of Spanish will I learn?
Related article: Español latinoamericano