As with many things in the new design, there are several ways to get to where you want to go. I will show the two easiest ways to get to the PM screen and send someone a PM.
First, you can click on your avatar that is always in the upper right corner. Once you do this, the dropdown box will pop up. The icon that looks like an envelope is what leads you to the PM page.
When you click on the envelope, it will take you to the Inbox of your private messages. On the far left, you can see the various other portions of your message screen: Inbox, Sent items, and Archive. What you want to do is click on the “New Message” button.
Clicking on the “New Message” button opens up the “compose private message” box, which looks similar to the “compose post” box you see every time you write a new post. The top box (circled in red below) is the address field where you enter the username of the person you want to send a PM to. The middle box is like the “subject” line of an email and the larger box is where you write your message.
When you start typing in the username, a list of suggestions will pop up, like this:
You can see that I just typed the letter “P” in the address field and it pulled up 6 posters that start with the letter “P”. If you see the person you are trying to contact in that list, you can just click on their name and it will automatically add them to the address field. Otherwise, you can keep typing. Of course, you want to make sure you type the name exactly with no typos. Otherwise, it won’t know who you are trying to send a message to.
The second method is to click on a person’s username within any thread. So, for example, when I click on your username in this thread, your User Card pops up. I can then just click on the “Message” button.
Doing this will automatically take me to the “compose private message” screen, only your username will already be in the address field. It will also include a link to the post I started the process from, because it is assuming that I am writing you a message related to what I saw you post.
You can always delete that link if you don’t want it there.
Does this clarify things for you? If there is some particular point in the process that is the source of confusion, let me know!