You've already got a login for the Admin side of Magento, but what about the other people in your team?
Magento has a built in functionality that lets you create new users that have access to the Admin side, but also limits what they can access.
First, we have to create a Role. A Role is basically a label/group you can apply to users that defines what they can see on the Admin Dashboard.
Navigate to System > Permissions > Roles.
Once you get to the Roles screen, click "Add New Roles". Note that Administrators is already added -- this is the group you should already be in. It gives full access to Magento.
After clicking to Add New Role, enter the Role Name. In this case, I've put in Sales Rep.
On the left side, you'll see some tabs. Click the "Roles Resources" tab.
You'll be taken to a screen with a lot of folders and check boxes.
It might seem overwhelming, but if you look closer, you'll notice that these are all the Menus and submenus at the top of the Admin Dashboard.
From here, you can check off the Menus that you want users in this group to see. Note that if you check off a Top Level Folder (a folder without indents, for example Sales in this screen shot), it'll automatically select all the submenus under it.
Click "Save Role".
Next, we'll create a User!
Navigate to System > Permissions > Users
Enter Account Information on the following screen.
Make sure the account is set to Active, or your user won't be able to log in.
In the next tab, click "User Role". You'll see the Role we created earlier in this tutorial.
Select the Role you want to assign to this User...
...Then click Save User in the upper right!
Now, when that User logs into the Admin Panel, this is what they should see:
I had only selected the Sales menu and all of its submenus, so that's all that should be visible to this user.