When creating a new user, there are two main ways. One is to copy an existing users profile and paste it onto a blank new user, the other is to create a new profile and build its permissions and access manually. There is more information available about how to create a new user
If you build up permissions manually onto a new profile, they will likely not have access to any menu options and the toolbar will appear empty, despite having access to the company and items within that company there are buttons visible on the toolbar to interact with.
To resolve this:
Log in as the affected user.
At the bottom of the toolbar, click My Preferences.
Select the check boxes visible here to enable the buttons.
Note: This will only enable the top level item. To enable the buttons within the task, click the yellow folder icon.
For example, you may enable the Toolbar item of Purchase Ledger, but you will still be missing the option for Suppliers unless you enter the yellow folder icon and tick the box for Suppliers.