Bulgarian, like a few other languages, has the concept of reflexive verbs, which roughly means that the object of the verb is the same as the subject. In practice, not all verbs adhere to that definition, and some are reflexive without any apparent reason. You will have to learn which verbs are reflexive and which are not. Some verbs will exist in both forms with a different meaning.
For example, казвам means "to say":
"Ана казва, че харесва да чете" - Ana says that she likes to read
But the reflexive form, казвам се, means "to be called":
"Аз се казвам Ана" - My name is Ana ("I am called Ana")
"Как се казваш?" - What's your name? ("How are you called?")
The "се" particle is normally included in the citation form of reflexive verbs.
As you can tell from the 2 examples above, the particle does not change according to the subject.
The particle normally appears before the verb, but as a clitic it can't appear at the beginning of the sentence and sometimes has to move after the verb:
"Аз се казвам Ана" or "Казвам се Ана"
Here are a few reflexive verbs that use the "се" particle:
- безпокоя (-и) се - to worry
- тревожа (-и) се - to worry
- смея (-е) се - to laugh
- шегувам се - to joke
- надявам се - to hope
- казвам се - to be called
- съгласявам се - to agree
- отпускам се - to relax
- гордея (-е) се - to be proud
- срамувам се - to be ashamed
- обаждам се - to call
- връщам се - to return, to go back
- местя (-и) се - to move
(to change location) - страхувам се - to be afraid
- наслаждавам се - to enjoy
("безпокоя се" and "тревожа се" are synonyms)
Examples:
"Не се шегувам" - I'm not joking
"Защо се смееш?" - Why are you laughing?
"Гордея се със сина си" - I'm proud of my son
Verbs used with the "си" particle:
There is another form of reflexivity that uses the си particle. This particle doesn't normally change the meaning of the verb but simply indicates that the action is done to the subject:
"Правя сандвич" - I'm making a sandwich
"Правя си сандвич" - I'm making myself a sandwich
"Те говорят" - They're talking (maybe to someone else)
"Те си говорят" - They're talking (to each other)
Sometimes, the си particle is just used for emphasis:
"Чета книга" or "Чета си книга" - I'm reading a book
The last two sentences basically have the same meaning, but the second one puts an emphasis on the reader enjoying the activity.
Here are some more verbs that are often used with си:
- мисля си - to think to oneself
- говоря си - to talk to oneself
- мърморя си - to mumble to oneself