Click the gear icon
Click Setup
Search "Data Import Wizard"
Click Data Import Wizard
Click "Launch Wizard!"
Under "What kind of data are you importing?", Click "Standard Objects"
Click "Accounts and Contacts"
Click "Add new records"
Add the CSV
Click Next
Map any 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.