What it means
にくい follows the masu-stem of a verb and means that the action is difficult to do. It often describes something that is hard because of its shape, condition, or circumstances, but it does not mean that the action is impossible. The form is an i-adjective, so it can be used in familiar sentences as にくい and in polite sentences as にくいです.
How to use it
Verb (ます-stem)にくいです
この瓶は開けにくいです。
This bottle is difficult to open.
Verb (ます-stem)にくい
この瓶は開けにくい。
This bottle is difficult to open.
Example sentences
このペンは細くて、字が書きにくいです。
This pen is thin, so it is difficult to write characters with.
このふたは固くて、開けにくいです。
This lid is stiff, so it is difficult to open.
この道は暗くて、歩きにくいです。
This road is dark, so it is difficult to walk on.
駅の案内板は雨でぬれて、読みにくいです。
The station information board is wet from the rain, so it is difficult to read.