Three Hundred
numeral
You have three hundreds. What does that come out to? Three hundred.
さんびゃく
The reading is a little bit weird, so be careful. You should already know the on'yomi readings, but the ひゃく rendakus to びゃく. This pattern will repeat itself with 三 + many counter kanjis that can rendaku, so pay attention for it as you read Japanese.
三百円です。
It's 300 yen.
大体三百人が来ました。
About 300 people came.
一年は三百六十五日です。
A year is 365 days.