How and where we can create various admin  profiles

If the users already have accounts you'll just need to change the Forum member Usergroup in the member profile > Account page on forum front-end. Or just navigate to Dashboard > Forums > Members admin page, find the member, click on "edit profile" link and edit Usergroup.

Forum Members are the same WordPress users. wpForo is fully integrated with WordPress and uses the same user resources, registration, and authorization system. 

activate the option of get the mail message in our Gmail telling that a new topic or a new answer has been posted and is ready to be answered by us?

you should fill the email addresses in the "Forum Admins email addresses " field.

And make sure the following two options are enabled

• Notify Admins via email on new Topic
• Notify Admins via email on new Post

The options are located in Dashboard > Forums > Settings > Emails admin page.

We are a team fof three people and we need that every time that some client post a new topic into our forum it will be sent to all three forum admins a message notifying that we have a new question to answer.

How and where we can create various admin  profiles an activate the option of get the mail message in our Gmail telling that a new topic or a new answer has been posted and is ready to be answered by us?

We wait your answer

Kind regards