Wǒmen chūfā ba.

我们出发吧。

Let’s get going.

Notes:

我们(wǒmen): we

出发(chūfā): set out, start off

吧(ba): a modal word indicating the sentence is a suggestion.

Example:

A: 队长，所有人都到了。

    Duìzhǎnɡ，suǒyǒu rén dōu dào le.

    Captain, all of us are here. 

B: 好。我们出发吧。

    Hǎo. Wǒmen chūfā bɑ.

    OK, let's get going.