There are two methods most used, one uses the attachments function which is just below the text block of your post, the other method which I prefer uses a third party photo hosting service such as Photobucket. The advantage of Photobucket is that you can post multiple photos anywhere in the body of your text by pasting the links where you want the photo to appear. The attachment method does not give you the option of where in the post to place the photo as the example under "Attached Thumbnails" shows. The photo within the body of the text was placed using the link method explained under Method 2.
This is very simple, below the text block of your post is the option to upload a photo. Go to browse, selected the photo file you would like to appear in your post then click upload. The photo will be added to your post at that point.
Additional info: If you are starting a new topic, the option to upload photos will autmatically apppear below the text window. If you are replying to an existing topic, you will need to click on the "More Reply Options" button in the lower right hand corner in order for thephoto upload feature to appear.
Photobucket.com is an example of a third party method. Here you would first upload your photo to their site following that you can select several methods of pasting a link to the photo which will appear in your post. The most preferred method is posting the IMG code link which will appear in the options block. The option block is brought up by hovering your mouse pointer over the photo. Highlight and copy the IGM code with your mouse then paste that link into your post. Very simple method, Photobucket also allows you to crop and edit the size of your photo on their site with those changes automatically being transferred to your post on the Machinegunboards.com site. Photobucket.com has an excellent HELP section that will show you all you need to do to post quality photos on this forum or others you frequent. Example of Photobucket hosting is below.
With either method some trial and error on your part will be necessary for you to learn how to do this.
Examples of the attachment method are below -