Category:High-performance computing

Hi! I am a real bnnegeir with wordpress, have no idea of how to program php codes. Therefore I kindly ask you if you can help me.Through the use of a specific plugin I have set my home page.Now, I don't want all the cadegories and subcategories to be shown at once in the sidebar, bur just the categories (main ones). Just by clicking on each category I'd like the subcategories links to appear. What should I do'Thank you for your kind help.