You can upload your contacts from a formatted .csv file directly to your Contacts by selecting the import button at the top of your Contacts table or directly to a Campaign. For information about how to format your .csv file for importing please see the help article Formatting Files for Uploading.
Once you have your file formatted correctly and are ready to upload to the Contacts table select Contacts from the navigation.
Then select the Import button.
Next, select the .csv file you would like to import.
Once you have uploaded your file you will then be taken to the field mapper where you can map the column headers of your .csv file to the associated Contact fields.
Once you select Import Contacts your contacts will begin to upload and will start showing up in your contact table shortly.