Go to Sign Up (/register) and fill in the form:
1. First Name, Last Name (if the business asks for them)
2. Email
3. Phone and Birthday, if enabled
4. Password and confirm it (minimum 8 characters)
5. Membership ID, if the business requires one
6. Check I have read and agree to the Terms & Conditions
7. Complete the CAPTCHA if shown
8. Click Register

On success you're logged in immediately and redirected to the page the business has configured (normally the storefront home). Behind the scenes the business is notified by email of the new signup, and — if the business's registration confirmation emails are turned on — you may also receive an email of your own confirming the account.