After click Add button, you can specify Account Access, Contact Access, Opportunity Access, Case Access, and Team Role. If your default sharing in OWD is Private for that object, you will see Private, Read-Only, and Read/Write options in the picklist. You can add up to 5 users every time you add team members manually.
But, the manual process is not fun when you need to add users into hundreds of account team members. So, here is the solution, use Data Loader to mass create AccountTeamMember records and AccountShare records.
1. Account Team Member
The API name is AccountTeamMember, you need to populate the following fields when mass inserts into AccountTeamMember:
Note: creating this record will not allow users added into AccountTeamMember to access Contact, Opportunity, Case if the sharing setting is Private. TeamMemberRole value can be different from values defined in Team Role.
Purpose: it will show user added to Account Team related list.
2. Account Share
The API name is AccountShare, you need to populate following fields when mass insert into AccountShare:
- CaseAccessLevel [optional]
- ContactAccessLevel [optional]
- OpportunityAccessLevel [optional]
You can set Private, Read-Only, and Read/Write in the above fields optional if default sharing in OWD is set to Private.
Note: user added into Account Share will access Case, Contact, and Opportunity records with Read-Only or Read/Write permission, even if it is not shown in Account Team related list.
Here is more information on mass create manual sharing rules with the Data Loader, click here.