Dipadee - first, load the photo from your camera to your computer, taking note of where you store it in the computer.
Post here. When you want to insert the photo into the post, click your cursor where you want to insert it. Then click on the symbol third from the right in the menu at the top of the window in which you're writing. It looks like a little green tree.
A new window opens. At the top, you can select whether you're uploading from your computer or an external side. Your computer is the default option so leave it as is. Click on Select. Then navigate to where you stored the photo on your computer and select the photo.
Then click Save.
The photo should appear within your post where you indicated with the cursor.