Please paint the inside of the box pink.
There is an enemy within.
The thoughts I hide inside myself were spelled out in my diary.
The kanji and the word are exactly the same. That means they share meanings as well.
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:
There's something inside and you wanna get to what's within. Look inside. Ooh, cheese (うち)! Your favorite. Ooh cheese, how I love you.