You can manage your users and contacts within your transaction. Please select Users & contacts tab within appropriate transaction and start adding or editing the information. To be able to add a user/contact please click Action button on the top of the screen and select Add user/contacts. In order to edit information please hit the Edit button from the right hand side menu.
As concerns Admins or users who have access to the contacts information adding and editing information for contacts can be done under the Contact tab. To be able to add a contact just lick the Add contact button. If information of the existing contact should be adjusted you need to select the required contact and hit Edit button from the right hand side menu.
Note: When you add a contact it become public for all users across your company to view. Please make sure you make it private if you do not want to share it. If you need to make a contact private please select available to: me only (private). The settings can be adjusted at any time by selecting appropriate contact and hitting Make private/Public buttons from the right hand side menu.
The below video will be useful for the users with Admin level of access.