know sb by sight 似乎相识，面熟

例句：

I know her by sight.

我与她并不熟识。

I have never met our new neighbours; I simply know them by sight.

我从未接触过我们的新邻居, 只见过面。

know the ropes 知道内情，懂得(某种行业的)窍门，很内行

例句：

We need to bring in somebody who knows the ropes.

我们应该找个懂行的人。

I've never used Linux so I really don't know the ropes of installation.

我从没用过Linux系统，所以我真不知道这个应该怎么安装。