Put your PC somewhere flat, please.
That girl put eight red marbles in a flat place.
Do you remember the name of the pasta that is thin, long and flat?
The kanji and the word are exactly the same with a little hiragana sticking out. Because the hiragana doesn't really indicate what it is, it's okay to assume that they share meanings as well.
Since this word is made up of a kanji plus some hiragana attached, 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:
Something is very, very flat. Perhaps someone who doesn't eat much, like a model? Which model? Let's imagine it's Tyra (たいら) Banks.