How can I add a sub-Category of a main section ?

You can add the main section of your store products through the following steps:
Go from the control panel to the products then sections and then click on the icon Create a new category ... Next image for clarification

Then enter the page category settings through which the name of the section is written in the languages listed on the control panel of your store and can add a picture of the section and write a description for it 

Note: After doing the name of the sub-section it must be chosen the name of the sub-Category through the icon of the original section to be followed ... Next image for clarification