Chat between agents and users is available through the chat widget in your portal/site you have embedded it on.
However, the tab isn't always there. It's only shown when the user has the correct permissions to use chat.
If you aren't seeing chat on the portal when you would expect to, check the following:
1. Make sure chat is enabled. In admin, check the control in Chat > Site Widget & Chat.
2. Check usergroup permissions for the user who is accessing the portal (in admin, check CRM > Usergroups > Permissions > Chat).
For a logged-in user to see the chat widget, they must be a member of a usergroup with the chat permission enabled.
3. If you want guests (i.e. anyone who's not logged in) to be able to see chat, ensure the Everyone group is enabled in CRM > Registration and that it has chat permission.
4. Are the correct chat department permissions enabled for at least one department in Chat > Chat Departments
5. Is an agent logged in to the agent interface with the correct chat and chat department permissions? Deskpro will show the chat widget if noone is online but it will revert to your ticket form.