The Word "Ostaa"

As I continued learning Finnish from the book we got from the full-time Finnish course, I found this interesting sentence:

Jos voittaisin lotossa, ostaisin ison talon meren rannalta. (conditional form)

Translation: If I won the lottery, I'd buy a big house on the seashore.

What I found odd was the use of "rannalta" (which literally means "from the beach").

In English and Indonesian, if translated literally to Finnish, it should be "rannalla" (which literally means "on the beach").

I asked hubby about this and turns out that for the word "ostaa" (dictionary form), you have to use the -sta/stä or -lta/ltä endings, since it means you're buying something FROM someone or some place.

Other examples:

a. Ostin ison sanakirjan kirjakaupasta. (I bought a big dictionary from the bookstore.)

----> The -n ending in "iso" and "sanakirja" means that you're buying only ONE big dictionary (only applicable for countable objects).

b. Ostin pienen talon Haastajantieltä. (I bought a small house at Haastajantie - Haastajantie is a name of a street)

c. Ostan käytettyjä vaatteita häneltä. (I'll buy used clothes from her/him)

----> Here I use the partitive plural for the object (used clothes).