If you are using Magento to create a website for a new store with very few products and no customers yet it may be easier to add the products individually. That said, if you are using Magento to create a website for an existing store you will most likely want to upload the customers and all product information (including images) from the old store. This article will teach you how to bulk upload in Magento.
How to Bulk Upload in Magento
To bulk upload customers or product information first create an import profile for each entity type you want to add to the site. First, navigate to System->Import/Export->Dataflow – Profiles in the admin panel. Next, click to ‘Add a New Profile’. Finally, you can either upload customers or product information.
How to Bulk Upload Customers

Your next step is to ‘Upload File’. This is where you will upload the csv file that contains all the customers you want to upload. Just make sure the the file has a header row which contains the names you listed in the field mapping and in the order you set the rows in the field mapping. Once you have uploaded the file click ‘save and continue edit’ and then click ‘run profile’. Select the file you just uploaded and click ‘run profile in popup’. The popup will give you feed back as the profile runs as to whether or not there are any errors.
Finally, assuming you don’t have any errors your customer table is now fully propagated with your old sites customers.
How to Bulk Upload Products and Product Images

The only tricky part to bulk uploading products is bulk uploading the images. In order to upload the images, first ftp all images to the media/import folder. It is very important that they are directly in the import folder, the upload will fail if they are in a subdirectory or any other location. In the csv file just use a backslash and the image name (eg. /sofa.jpg). Magento puts the images in the right place and adds the correct location under the product information when the profile is run.

If you find you need expert help on how to bulk upload in Magento contact Brian Wade at https://cybersolutions-llc.com.