you need to assign a role. For SMC there are already a few roles available in your User Manager. - Management Console: Advanced - Management Console: Content Management - Metadata Server: Operation - Metadata Server: Unrestrictet - Metadata Server: User Administration
You can find a short description of the abilitys they give in the description-field of these roles. To give Access to Plugins, I would start with the "Management Console: Advanced" role. If you dont want to give Access to all Plugins, make a copy of this role and remove the unwanted Plugins in the function-tab and assign this role.