Unable to use the internet on my MacBook or sign out to reset it
You must provide much more detail about your MBAir and the problem in order to get help here. Just saying that something doesn't work gives us no information on which to help.
Writing an effective Apple Support Commun… - Apple Community
"Internet not working on MacBook air: Unable to use the internet on my MacBook or sign out to reset it"
-------
Sign Out of what? A network? You might need to be an administrator user to have the ability to perform his.
Connect your Mac to the internet - Apple Support describes the fundamental steps.
As MartinR alluded to some context is likely to help.
Internet not working on MacBook air
