These are the steps to share files outside the company.
  1.    At the top of the Documents library on your SharePoint site, click New, and then select Folder.
  2.   Give the folder a name, and then click Create.
  3.    Upload the files you want to share to the new library, or choose New to create new documents directly in the library.
  4.    Select your new folder in the Documents library, and then click the Share button.
        
  5.   In the Send Link window, click the list at the top, choose Specific people, select Allow editing, and then choose Apply.
        
  6.   In the Send Link window, enter your customer's email address, type a message, and choose Send.
  7.  Your customer will receive an email with a verification code, which they'll need to send to themselves to access your folder. If they can't find the email, they should check their Spam folder.