This is how do we say in Russian 'he/she has' and 'I/we have'. This is the way to express possession.

Debs, у меня экзамен - I have an exam у меня болит голова - I have a headache у меня есть три рубля - I have three roubles у меня гости - I have guests у меня хорошо - it's good at my place У нас солнечно. А у вас? - it's sunny here (where we live). What about you/Italy/the place where you live? Literally: "by me: [there's] guests/exam" "by me: [there] is 3 roubles" "by me: is-acheing head" "by me: [it's] good/sunny" It is rather universal construction, it informs you that what's going to follow is news about 1. me, 2. my life, 2. or my place. In most cases its English counterpart is "I have", "we have", "John has" but not always.

As for "why". Russian word order is free, so we use it to express what is the "topic" and what is the "comment" (what we are speaking about, and what are the news about it). If I said моя голова болит - my head is acheing It would sounds like news about my head, not me! We want to have "I" in the first place. English speakers too. English speakers achieve this with auxiliary "have": I have a headache. Russians aren't into auxilliary words:) So we say "by me" and then then news: "head is acheing". As it is more comfortable to have the verb second, we say "is acheing head". English does something similar with "there" in "there is a cup on the table": 'there' is a word for a place of action. But it is auxiliary here. Russian would do it in a simpler way: на столе стоит чашка - "on table is cup".

"Y" is used as "from" in English

"Y" is used as "from" in English