MyBB Community Forums

Hello I want to learn how can I send mass mails to all members of forum (who selected that its okay to get e mails from admins)

and in which format I should be doing that? Is there a program etc. for that? I want it similar to newsletters game companies have.

forum admin panel >> users & groups >> Mass Mail

more details => Mass Mail - MyBB Documentation

see also Newsletter plugin

Make sure you use good smtp server if you want all mail's to deliver inside inbox and not spam.

If you are using default webhosting php mail server then chances are they wont get delivered to end user.