Try using the words 'error code 80 steam' on google and you will find enough results.
By searching for a minute I found out the following:
- It looks like it is a generic steam error used for multiple types of errors.
- There is no real fix, since the exact cause is unkown.
- To play a game, simply exit and restart steam.
- Some people restarted their pc and the error was gone.
Now I haven't investigated this thoroughly, but please try the last two and post if you can now play or not.
Next time you could also post which things you have already tried to fix an error.