@pekoe01
Here is the way to post so that a member will get a notification of your post:

Underneath the post you want to respond to click on the "Reply" button and then post your question or comment in the box that will appear. Also, you can begin your post with their username. For example, look at how I started this post to you, I used your username with the "@" sign in front of it. After you finish your post click on "Reply."

Both of these methods will give the recipient a notification that you have responded to their post.