Each post is within a topic page. In the main topic page (which lists the most recent posts) the sub-topic page is displayed as the title of each post and at the bottom of each post (both of which are linked by a mouse click).
You can enter a link into your comment by simply copying the URL address of the website and pasting it into your comment. You can do this by using the mouse menu (right button), or Control C for copy and Control V for paste.
Alternatively, to link from a text in the comment, for example “TEXT”, to an address you want to link to, for example “ADDRESS”, put the address and link text (using TEXT and ADDRESS as examples) into a coded line using HTML code. Write a coded line without spaces, except to separate code elements, as here before “target”; as in this example: