expression, noun
learning by watching and imitating; picking up by observation
Refers to acquiring a skill or knowledge simply by observing someone else do it, without formal instruction. Often used when someone successfully (or surprisingly) does something just from having seen it done.
彼は見よう見まねで料理を作った。
He cooked the dish just by watching and imitating.
見よう見まねで始めたギターが
I started guitar just by watching others, and now it's my hobby.