There are two ways to gather applications for accreditation to your event edition.
An event organiser can open a specific category for public applications, for example to welcome applications for press accreditation. If that is the case, you can invite people to go to your organisation URL [your-organisation].accredion.com, where they can create an account. After creating an account and loggin in they can apply for accreditation.
Alternatively, as group manager you can send out personal invitations for your event edition via your group menu Accreditation > Invite people.