without making much noise

I slipped quietly out of the back door. 我悄悄地溜出了后门。

He is a quietly spoken, thoughtful man. 他是个话语轻柔、体贴周到的人。

in a way that is not obvious to other people because you do not say much

He is quietly confident that there will be no problems this time. 他心里暗暗相信这次必定没有问题。