When a user start to use AAC they need help to get started. The best way you can help is by using the AAC solution yourself when you talk to the user. Talk about everyday things like what to have for dinner. You do not need to say everything you say also with the AAC solution but say some of the words with the AAC solution and let the user see what you are doing. This is called modelling.
This video and a lot more you find in the free app Pathway for Core First