Hard to do; indicates that performing an action is difficult or awkward (attaches to verb stems, e.g., 説明しにくい).
このソフトは使い方が複雑で、初めての人には操作しにくい。
This software is complicated to use and hard to operate for first-time users.
彼には頼みごとが多くて、直接頼みにくいと感じる。
He has many requests, so I feel it's hard to ask him directly.
この問題は説明しにくい部分があるので、図を使って説明します。
There are parts of this problem that are hard to explain, so I'll use a diagram.