When you are writing a post look directly beneath and there is a box that says "Attach Files". Just click on that and a "file upload" box will appear. Choose the file(s) from your computer and click "open". A thumbnail will appear with "insert" in the top left corner. Click on that and "Full image" will appear underneath. Click on that and your image will be inserted into the post you are editing. If you change your mind, just click on the trash can icon in the top right corner and it will delete it.