Question: I wish to know how to put so many subjects like Joomla' s front page (instead of having only 3 news by default)

Answer: Go to the backend of your website -> at the top of the page on the left side, hover over  menu -> in the dropdown box, select mainmenu -> when mainmenu opens, select home -> when home opens, look on the right hand side under parameters -> you will find leading, intro and columns. Change the inro to the number of articles that you want.