Not complicated; easy or simple. A very commonly used na-adjective for everyday situations.
この問題は簡単だからすぐ解けるよ。
This problem is easy, so you can solve it quickly.
朝ごはんは簡単に済ませた。
I had a simple (quick) breakfast.
説明は簡単で構いません。
A brief/simple explanation is fine.
初めてでも簡単に使える設計だ。
It's designed so that even beginners can use it easily.
Brief, quick, or light—indicating something done in a short time or in a concise manner (e.g., 'do something briefly').
会議は簡単に済ませて昼ごはんに行った。
We finished the meeting quickly and went to lunch.
説明は簡単にお願いします。
Please keep the explanation brief.