You will come to know whether you already have an existing profile with the organization or not, when you start applying for a job.
For instance, if you do have a profile, while signing-in, after entering the email address, the system will prompt to enter your password. This makes sure that you have an existing profile with the organization.
If you do not have an existing profile with the organization, then after entering the email address, the system will navigate you to the page where you can create a new one.
Note: Your profile can be linked with only one email address. If you have multiple email addresses and if you are unsure about which one was used to create the profile, then the best practice is to try all email addresses one by one to check whether you have an existing profile with the organization. Please do not create multiple profiles with different mail addresses in an organization. So please make sure that you do not have an existing profile with the organization before creating a new one.