How can we make diagrams in a Microsoft Word document?

you can use "smart art" or "chart" which is related to excel table where you can write your data.

by inserting smart art or shapes and add text to them

Select (insert option) from  the list then press on (chart option) or click on (smart art option) choose any type 

making a diagram in Word. Open the Word office, click on the Insert Button then click on shapes you will see many shapes tool then use them according to the picture on your mindset.

by inserting Smart Art, Shapes and Symbols, etc.