Pleasant, delightful, or amusing; a na-adjective describing something that makes one feel happy or entertained.
彼の話はいつも愉快で、みんなが笑ってしまう。
His stories are always amusing and make everyone laugh.
愉快な気分で週末を過ごした。
I spent the weekend in a pleasant mood.
その映画は愉快で軽い気持ちになれるコメディだった。
That movie was an amusing comedy that lightened my mood.