You can watch it for free.

你可以免费观看奥运比赛。

A It’s so difficult to get Olympic tickets.

A 买奥运会的门票非常难。

B I know. But remember – there’s one event you don’t need tickets for.

B 我知道。 但是记住——有一个赛事你不需要门票就可以观看。

A What’s that?

A 什么比赛?

B The marathon.  It goes all through the streets of Beijing. You can watch it for free.

B 马拉松比赛。马拉松比赛全程都要穿过北京的街道。你可以免费观看。

If something costs nothing, you can describe it as ‘free’.

如果某事不需要任何花费，你可以把它描述成“免费的”。