When you open the CRM module, the Contacts tab will be open:

Tap

to open filtering.
Tap a contact's name to open its details or tap Add new to create a new contact. The contact details will open:

Tap each field to edit it. Unsaved changes are in red.
Tap Account to bring up a menu where you can choose to open the account details or to change the account associated with the contact.
Tap Phone or Email to bring up a menu where you can choose to start an activity or to edit the number or address.
Tap Save in the top right corner to save your changes.
Click

to display the history of changes to the contact.
You may have more fields to fill out depending on your specific set up. Contact your manager if you are unsure how to fill them out.
The contact's past Activities, Tickets and Attachments are below. Toggle between them by tapping the tabs.

Tap an activity to open its details or tap a ticket to open it in Tickets. Tap an attachment to download into your mobile phone.