After clicking the start now button, you can use your gmail, linkedin, apple id or facebook account BUT make sure to have a decent, formal and identifiable email or account. If you do not have such an account, i suggest you create a new email account to indicate and identify you. Note that the badge you will get here is accepted and accredited by companies using Salesforce CRM.
Next, you will need to fill up your personal information. Trailhead will create a profile URL for you; set the PUBLIC PROFILE ON.
Next, fill in the information given below
Company Name: Mapua Dev Batch 1
Job Title Student
Role Name: Student
Relationship to Salesforce: Customer
Then click Done.