Ocean
Sea
noun
The kanji and the word are exactly the same. That means they share meanings as well.
うみ
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
You visit the sea. Strangely, it asks you who is visiting. You're so full of yourself (even in front of the sea/ocean) that you reply: "um, me?" (うみ). Imagine yourself feeling this full of yourself.
海で泳ぎました。
I went swimming in the sea.
海の公えんで、先生が学生に話しています。
The teacher is talking to her students in Marine Park.
映画「水の世界」は、実は、海の底に住んでいる超頭のいい魚によって書かれた作品だ。
The movie Water World was actually written by a race of super-intelligent fish that live at the bottom of the ocean.