It is basically categorical and quantitative data. I will make it simple for you.
Measures -> Quantitative -> Numbers (e.g: Sales, Profit, etc.)
Dimensions -> Categorical -> Text (e.g: Name, product, etc.)
Tableau identifies it the same way by breaking out the data like this.
Dimensions are essentially self-explanatory but measures are not. For example: You can’t just view profit, you will be like - profit of what? And I will be like - profit of shampoos!
So, you need a dimension to attribute measures.