What is the government supposed to do with regards to civil liberties?According to the Constitution.
The main thing that the government is supposed to do with regard to civil liberties is to avoid infringing on them. In other words, civil liberties are our right to be free from government interference in our lives. Therefore, governments role is to make sure it doesn't violate our civil liberties.
If you look at the Bill of Rights (where most of our civil liberties are spelled out), you see that it talks about what the government must not do, not what it must do. So when it comes to civil liberties, government's role is mostly negative. It must be sure that it does not prevent us from practicing our religion. It must be sure that it does not take away our right to free speech. It must be sure that its officials do not search us or our houses without probable cause.
There are a few "positive" things government can do (like providing poor defendants with a lawyer) with regards to civil liberties, but mostly it is just supposed to make sure it doesn't infringe on those liberties.