if i want to connect a usb port to my macbook air, is there an attachmnet i can buy?

If you bought a new Mac, it'll have only usb-C ports. If you want to connect e.g. an external drive with a usb-A port, you can use an adapter like this https://www.apple.com/shop/product/MJ1M2AM/A/usb-c-to-usb-adapter?fnode=62e4ebaac56261393e29ae76328cc585a9ffcfb6fbb95e3e06108d3b99a68064c5e174495cc48c8ef61d2fac2dbaf1fd5207dadaa255c25cf8c5d534c09ea447c9ab69295609537dbb5ebccc60f93a9c2c88e2aad3b94c0efd94d1b2d35fe1fa55048c496483888946ce0723285793fb

If you want to connect more than one external device at once: look for an adapter or hub with multiple usb-A ports

What year MBA?

Are you wanting to make available a USB-A type port for an older device maybe? Your MBA has USB ports but various years have various types.

New or used? If used what year?