1An i-adjective meaning 'easy' or 'simple to do'. As a standalone word it is somewhat literary or dated — modern speech usually prefers 簡単 or 易しい — and it survives mainly in set phrases (e.g. 言うは易く行うは難し, 'easier said than done').
言うは易く行うは難し。
Easier said than done.
彼にとって、そんな問題を解くのは易いことだ。
For him, solving a problem like that is an easy matter.
口で言うのは易いが、実際にやるのは大変だ。
It's easy to say, but actually doing it is hard.
2Attached to a verb's masu-stem to mean 'tends to ...', 'is prone to ...', 'is apt to ...'; often describes an undesirable tendency or likelihood. Usually written in kana.
白い服は汚れやすい。
White clothes get dirty easily.
彼は感情的になりやすい。
He tends to get emotional.
この季節は風邪をひきやすいので気をつけてね。
You catch colds easily this time of year, so take care.
3Attached to a verb's masu-stem to mean 'easy to ...', i.e. that an action is simple to perform. The opposite is 〜にくい. Usually written in kana.
この本は字が大きくて読みやすい。
This book has large print and is easy to read.
このアプリはシンプルで使いやすい。
This app is simple and easy to use.
先生の説明はいつもわかりやすい。
The teacher's explanations are always easy to understand.