osCommerce is a A power-user shopping cart with a big variety of modules and support of almost every payment gateway.
1. log into your cpanel DOMAIN.COM/cpanel username password
2. click the Fantastico button bottom left (blue smiley face)
3. once in Fantastico find the osCommerce link on the left side and click it.
4. click new installation
5. read and follow the instructions carefully choose your root domain domain.com by leaving the directory blank or name a directory ex.domain.com/myshop.
6. Pick an administration and password for your osCommerce admin panel
7. pick no for ssl certificate.
8. click install osCommerce
9. now you have to click finish instillation
10. Final step click here to protect the administration area. Your done.
P.S Book mark the administration area you will visit that url frequently.