Loose, Mild, Gentle
な adjective
This is the na-adjective version of loose, so that means this word means loose or mild or gentle.
ゆるやか
The reading comes from what you learned with the kanji.
その小川が緩やかに東にカーブしているところがあるんだけど、そこが釣りの穴場なんだよ。
The stream curves gently towards the east and is a good fishing spot.