I can't buy anything for some reason idk why
unable to purchase stuff
The Classic operating system which this forum is about is very old. There are some browsers like Wacom Mozilla and Tenfourfox available for Macs compatible with Classic, but running a newer Mac OS X, but many sites no longer support these. iCab is another old browser for secure transactions.
Without knowing which Mac model you have, it is very hard to tell what you need to purchase stuff. Also not knowing the website in question, won't let those of us with older Macs to find out if there is an older browser compatible with it.
Classic is available for Macs like the one on your avatar, and other Macs that do not have the Intel CPU. By the same token none of them can run Mac OS X 10.4.11 or higher with Classic in virtualization, or Classic as a boot operating system with anything higher than Mac OS X 10.5.8. To learn which does what, see this tip: