Importing a CSV File
In the plugin page, select your file. If all the files share one Item Type, go ahead and select that Item Type from its respective menu (similarly if you want to add all items to one collection). Go ahead and make the items public. The rest of the delimiter options should be right where they are. Click Next.
Here, you will tell Omeka what columns correspond to which elements. Select each corresponding column to each Element. If you don't select an element, Omeka will disregard that entire column. If you have a tags column, just check the "Tags?" checkbox.
Once you're done, import the CSV. It will take you to a status page, which you can reload for updates. The upload shouldn't take very long.
Once uploaded, take a look in your Items. They should all be there, ready for specific editing and file-adding. Good luck!