How to create inner join relationship in data model?

jaryszek You must have some common key columns in both the tables so based on that you can simply join in Relationship tab of PBI desktop. (refer below screen  shot)

Go to Relationship tab >> Click on Manage Realtionship >> New >> Then select table name from drop down and select key column (Category column in my case) and similarly select second table and do the same. As per your need select Cardinality and hit OK.