Preocupar is to worry, however, preocuparse a pronominal verb also to worry or to be anxious.

Worry as a noun is preocupación.

Don't know if this answers your query.

I think that "preocuparse" is used when you want to say, "I am worried;" for example, using "me preocupo" as an alternative to "estoy preocupada" to say, "I am worried." Sometimes in Spanish reflexive verbs are used for feelings like this and the literal translation to English doesn't make very much sense. "Preocupar" is used as more of an action verb than a feeling one - for example, if you were to say "él preocupó," it would mean "he worried."

¡Espero que yo te haya ayudado!

Preocupar = to make others worried
Preocuparse = to worry

And now the explanation:

Many Spanish verbs are transitive, i.e. they need a direct object. For example:

' romper = to break (something)
' hundir = to sink (something)
' quemar = to burn (something)

These transitive verbs assume that there is something or someone (an object) upon which the action is applied, so if you say "el barco hundió" (the ship sunk), you cannot assume that the ship just couldn't float anymore, since the verb is transitive. The sentence is incomplete in Spanish because after hearing "The ship sunk", any native would be expecting an object, i.e. something to sink. So, the ship sunk... another ship perhaps? Without an object, the sentence sounds incomplete and makes no sense. Spanish's solution for this is add an extra "se" that turns the verb into intransitive, so no object is expected, and everything is assumed to be related to the subject. For example, "El barco se hundió" would be "The ship sunk", but this time, the "se" tells us that this ship is not sinking other ships or anything else, but it is just sinking, nothing more.

The verb "preocupar" requires someone to make worried (the object). You can make your parents worried (preocupar a tus madres), and things can make you worried (la situación me preocupa). However, if you are just worried, with no object (no one to make worried), then Spanish resorts to this "se".

Me preocupo
Te preocupas
Se preocupa
Nos preocupamos
Os preocupáis
Se preocupan

This "se" has no translation in English, since "worry" can be used as intransitive in English, but "preocupar" cannot without this pronoun.

As Eddy mentioned, this "se" is generally called "pronominal", and more intuitively, intransitivizer "se" by other authors.

Marco,
I can help you. preocupar is a transitive verb, for example, sth worry sb. while preocuparse is the reflexive use. We usually say preocuparse de ... which is the English equivalent of be worried about ...

you can say preocupado or nervioso. they both mean worry. but i would go with preocuparse.

Thanks lazarus, I found that really helpful.

I must say Lazarus that is one of the best explanations I have heard on this particular point with which I have had trouble for years. Thanks.

Me too.

Thank you, lazarus for your explanation. I want to make sure if I got you correctly after I read it. My understanding is that "me preocupo" means "I am worried", correct?
If I want to say "I worry", should I say "se preocupo"? It's very common to say "I worry about something" in English and just want to know the correct sentence.
Será muy útil si puedes dáme más ejemplores.

Muchas gracias,

Marco

Thank you, Luis for your reply.

Marco

Me preocupo (por algo/alguien) = I worry (about something/someone)
Te preocupas (por algo/alguien) = You worry (about something/someone)
Se preocupa (por algo/alguien) = He/she worries (about something/someone)
etc.

Preocupo (a alguien) = I worry/bother (someone)
Preocupas (a alguien) = You worry/bother (someone)
etc.

Estoy procupado por = I am worried about

Is that enought'

Muchas gracias, lazarus. Your reply really made sense for me. It's really, really helpful and I am clear now. It is enought.
By the way, honestly only telling me the grammar tules might not help me a lot because like what I said before that English is not my native language and I might not be able to understand the rules correctly and easily, but giving me rules and examples would be really, really helpful for me.

Thank you, lazarus.

Marco