Almost every entry you'll see will have links to read comments and reply to the entry. Some entries or journals will have commenting disabled or restricted to certain users, depending on the wishes of the journal owner. But if your friend has commenting turned on, you'll see something like this attached to the entry:
Comment links may look different depending on the journal that you are in. Sometimes people customize their comment links so that they have clever sayings instead of plain ordinary "post comment".
See my comment links, for example:
My comment links are translated into the "Baaah" language for relatives of mine who are more familiar with this language. But for those of you who don't speak "Baaah", you'd click on "Baaaaa" to leave me a comment.
You can write HTML in comments if you want to change the look of your text. But if you don't know how, you don't need to bother - comments will work with or without HTML, just like your entries do.
Any questions about commenting? Ask them here! (You will need to comment in order to do so.)
If you can't leave comments or if you have questions about something else, please see our community profile for ways to get help using your new journal.