When you are writing your post you will see a tab below where you type that says Upload Attachments. Click on this tab then click the "Choose File" button. Select the file you want to upload and click the "Add the file" button. Once you have selected all the photos you want you can click submit to post and they will show as attachments at the bottom of your post or you can place them inline wherever you want within your post. The files size limit to display without having to click on the image is 200K if I remember correctly. I have found that images sized to 800 x 600 pixels display the best.