i have the oldest macbook air and can't really do anything on it. how do i install the newest macbook download (so it looks like the newest one) on my old macbook?

he current macOS Monterey can only be installed on 2015 or later MacBook Air models. See: How to upgrade to macOS Monterey - Apple Support

What is the model year of your MacBook Air and what operating system is currently installed? Both are available at Apple menu > About this Mac. The original (2008) MacBook Air cannot be upgraded beyond Lion 10.7.