You can import contacts into Makerble via http://www.zapier.com
Steps
Contact helpdesk@makerble.com to request Early Access to use the Makerble Zaps on Zapier
Go to the Create Zap page
Select the source app you want to use as your Trigger, e.g. Google Sheets
Sign in to that other App if you are not already signed in
Select Create Beneficiary as the Action on Makerble
Press Continue