If you are new to Dynamics AX and work on the functional side of things. If you have to write specifications for a modification you want, or you are investigating a data issue, or understanding the data model to investigate for reporting and BI then there are some good tools in AX to allow you to understand what is in the data model behind what you are looking at. There is a quick walk through of some of the tools.
Remember if you are poking around the data and have access to these tools then you want to make sure you are doing this investigation on a test environment to avoid the risk of changing something you didn’t mean to change. The table browser has edit, insert, delete capabilities if the data model and validation code allow so keep that in mind.
If you want to see ER diagrams for AX then you could start here.
These are published diagrams so they are static at the time of published so maybe not include CU updates and are specific to a version. In this case they are specific to R2. So if you are using R3 then good chance they are still valid but if there is changes or new functionality you won’t find these here. As well if you have ISV/partners solutions in your environment then you won’t find the ER diagrams in the Microsoft documentation so good thing is that you have the tools to investigate.