Hundred Million
numeral
The kanji and the word are exactly the same. That means they share meanings as well.
おく
The reading is the same as the one you learned with the kanji, presumably because it's normally attached onto other numbers to signify how many hundred millions of ____ there are.
私たちは、今年は五億円を売り上げました。
We made five hundred million yen in sales this year.
あのドクターは、三億ドルの車に乗っています。
That doctor drives a three hundred million dollar car.
私は友達が二億人います。
I have two hundred million friends.