Hey @Batman welcome to the Asana Community Forum
The first step will be setting up a workspace or an organization: Workspace basics | Product guide • Asana Product Guide
You would then be setting up Asana teams and projects and if you are the admin you have access to everything.
The same applies if you are project or team owner then you would also see all tasks.
Here is an overview on permissions: Permissions overview • Asana Product Guide, Project permissions | Product guide • Asana Product Guide
Here is a nice post from Bastien as well: Who sees whom, a guide to guest visibility with Batman & Robin
Hope that helps