To have an image appear in your post on the Forum you need to tell the Forum software where you want the image to display in your post and where to get the image the you want to display. Depending on where the image is located on the internet as to how easy this can be, however hopefully this article will give you the basics to understand what is going.
Being able to take a photo from your computer or device and upload it directly into your post can be done by using the Attachments feature and this article explains how to make it happen. Images must have a file-size of less than 3MB or they will be uploaded and then you will receive a message saying the file is too large, wasting your data allowance if you are using a phone etc. and you will need to resize it and try again.
As part of the new integrated Club site and Forum is the inclusion of a Photo Gallery where members will be able to upload images into organised areas for browsing and also used in their posts on the Forum. At the time of writing this it is still under development so the details below may change.