Click Setup
On left hand menu, search "Data Import Wizard" or go to Administer -> Data Management -> Data Import Wizard
Click the "Launch Wizard!" Button
Under "What kind of data are you importing?", Click "Custom Objects"
Scroll to and Click "Products"
Click "Add new records"
Drag & Drop CSV file or Click CSV button
Click Next
Map any relevant unmapped fields
Click Next
If everything looks like the image below, click Start Import
Click OK
When done (Progress 100%), you will see records processed.