I need to create a website for a client using Drupal 7, the only problem is that I don't know how to handle multiples login forms and permissions.
The goal is that A type of user must be allowed to browse and do some stuff on the website but they can't post offers, however B type of users can only post their offers and manage their contents, the system is just as Upwork.
How can I achieve this ? I'm not good at PHP but I know how to use Drupal, so are there modules that can help me to do what I want?
This is exactly how Drupal works by default using role based permissions. You won't need to install a module or have different login forms.
Start by creating different roles. RoleA can view certain content types and maybe post comments. RoleB can do everything RoleA can do plus post offers and manage their own content. You can control create/edit/delete permissions by content type. It can all be done using the point and click admin interface.