To start understanding how all work you should know first, that WordPress User Roles like subscriber, contributes, author, editor, etc don't have any affection in forum accesses. They are not used in forum. They are synched with forum Usergroups. And forum Usergroups are used to get different accesses to different forums. Please follow the steps below to see wpForo Usergroups and Forum Accesses...

Step 1:  Understanding, that in forum there are no Roles like Subscriber or so. wpForo has Usergroups for this purpose. And each Usergroup is synched with WP User Roles. For example Subscribers are the same users with Registered Usergroup. The Registered Usergroup is the same Subscriber User Role. You can see that they are synched together in Forums > Usergroups admin page. So saying Subscriber Role you should understand Registered Usergroup in wpForo Forum.

https://wpforo.com/wp-content/uploads/2018/09/wpForo-Registered-Usergroup-is-the-same-WP-Subscriber-User-Role.png

• Forum Usergroups Doc: https://wpforo.com/docs/root/members/usergroups-and-permissions/

Step 2: wpForo forums have permission settings in Edit Forum screen. Edit the forum and use these settings to control Usergroup accesses and privileges in that forum. Each Usergroup has some Forum Access set in each forum. For example The Registered Usergroup ( Subscriber User Role) has Standard Forum Access by default in all forums.

For example if you don't want users with Registered Usergroup to open new topics in some forum, you should edit that forum and set Read Only forum access to the Registered usergroup that forum. Then navigate to Dashboard > Forums > Dashboard and click on button.

https://wpforo.com/wp-content/uploads/2018/09/wpForo-Usergroup-Forum-Access-setting.png

• Forum Accesses Doc: https://wpforo.com/docs/root/wpforo-settings/forum-accesses/

Step 3: Understanding the Forum Accesses. Forum Accesses are set of forum permissions:

• Can view forum
• Can create topic
• Can view topic
• Can post reply
• Can view replies
• Can edit own topic
• Can edit own reply
• Can delete own topic
• Can attach file
• Can view attached files
• etc..

For example, if you set the "No Access" forum access for Registered Usergroup in X forum. All users who are in Registered Usergroup will not be able to view that forum and topics in that forum. Because the "No Access" forum access permissions are set this way by default:

• NO Can view forum
• NO Can view topic
• NO Can view replies

You can find all permissions of No Access forum access in Dashboard > Settings > Forum Access > No Access (edit) screen.

https://wpforo.com/wp-content/uploads/2020/04/wpForo-No-Access-to-Forum.png

• Forum Accesses Doc: https://wpforo.com/docs/root/wpforo-settings/forum-accesses/

Step 4: Secondary Usergroups have the same power like the Primary Usergroup. wpForo allows setting multiple Usergroups to the same user. For example if Usergroup A has access to Forum A and Usergroup B has access to Forum B and you want User AB to have accesses to both Forum A and B you should set User AB primary Usergroup A and Secondary Usergroup B or vice versa.

• Secondary Usergroups Doc: https://gvectors.com/using-secondary-usergroups-in-wpforo-wordpress-forum-plugin/

Good Resources:

• How to create private forum: https://gvectors.com/how-to-set-up-private-forum/
• Hot to enable guest posting: https://gvectors.com/how-to-enable-guest-posting-on-wpforo-wordpress-forum-plugin/