Hi,
You might find these knowledgebase articles on adding products helpful:
- How do I add products to my store (covers all 3 methods, the import is right at the bottom of the article): http://www.americommerce.com/kb/?f=312
- Data Imports: http://www.americommerce.com/kb/?f=144
Some of the snapshots in the second kb are in the process of being updated (so depending on your version you are on, these may or may not match). But the steps should be helpful in outlining the method.
Cheers,
Manjula