You will use your social security number.  However, if you plan to continue in the future with your business having an EIN will help in that you can open a bank account, reduce the number of time you have to use your social security number and protect it as your business grows etc.   To get an EIN on the IRS website Apply For EIN - Employer Identification Number, during their open hours listed on the site.  You will get the number the same day.