You can guess this is an adjective from the い at the end. The meaning for the kanji is noisy, so the adjective version is also noisy.

喧しい is a casual but emphatic way to say someone or something is too noisy. It's often used in Japanese comedy and variety shows, so depending on the situation there can be a playful vibe to it. You can even use it in a figurative way to describe someone who's being overly picky, fussy, or annoying about something particular (they're being "noisy" about insignificant details). Note that in everyday situations, you'll often just see this word written in kana as やかましい.

Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn the やかま reading with this kanji, so here's a mnemonic to help:

My noisy mom has earned the nickname yak-a-Ma (やかま). She's always yakking about my life choices. "Yakka yakka yakka," Ma says.