First, go to the homepage and click on 'Authors' (found in the lower left corner of the page). You will then be taken to a page full of journal covers. Clicking on a cover will show you all the necessary information you require to submit an article to that particular journal, including who you need to contact and how to format your work.
All Tsinghua Journals encourage online submission. If the journal you are interested in is accepting submissions in this way, you will see a ' Submit a Manuscript ' button on their home page. Click on this button for more information.