What are the effects of an asteroid collision and how can we prevent a future one?

As you may or may not have guessed absolute devastation.

Explanation:

(although it depends on the size.)

For reference the asteroid the hit the plant 3.26 billion  years ago it was hugely devastating and wiped out more than half of life on earth.

Simply put Small chance of human survival today.

However, On a much brighter note there are studies being done right now to see if there is a way to stop that from possibly from happening again in the future or slow it down when it happens, change it's trajectory from the earth, absolutely demolish it to smithereens and etc.