Ha! I just saw now in another post where someone mentioned you had a D7100. Wish I'd seen that one first. Anyway, nice camera! Once you get the hang of it (which isn't hard) I'm sure you'll be amazed at what it can do!
Posting your pics is a piece of cake. Assuming you have pictures saved somewhere on your computer, here's all you do:
See that row of stuff just above where you start typing your posts and replies? In the middle you'll see boxes that say "Font" and "Size", and to the right of that there's a smiley face and then a box with 5 pictures (the last picture being a speech bubble). If you click on the middle picture, which looks like a box with a dot at each corner, that's what lets you add a picture.
When you click it, a box will pop up. At the top are two tabs. One says, "From Computer". The other says "From URL". If your picture is stored on a website, click "From URL" and put the full URL in the box and click "OK" at the bottom. You picture will be inserted in your comment.
If your picture is stored on your computer, click "From Computer". In the middle, you will see a button that says "Browse". Click that, and a pop-up box will appear with your computer's files that you can scroll through to find the picture you want. When you do, just double click on it. The click "Upload" in the box, wait a moment, and your picture will be inserted in your comment.
If you want your picture bigger than the tiny picture it gives you, double-click with the left mouse button while your cursor is over the picture. Another box will pop up, and you will see one of the options is "Size". Just choose Medium or Large, and it will make your picture...medium or large! Hooray!
That's all you do.
Why don't you give it a try now, to see if that makes sense. Assuming you've taken a picture already and it's stored somewhere either on your computer, or on the web, that is.