It's very simple my friend. Go to
www.photobucket.com and register. Once you've done that you can go ahead and "upload" photo's to your album. Once you have the photo's you want to post uploaded, just click on a photo you want to post on here. On the right side of the photo/screen there will be a list of the Photo's "links" There is one near the middle that says "DIRECT LINK" click that and it will automatically copy that URL for you (it will look just like a website url cuz that's what it is) then you just click back over here to GMT400 and in the reply box here you will see the little "tree" icon in the toolbar ontop the reply box it will say "insert image" when you position the mouse over it. Simply click that and paste the URL (direct link) that you copied over from photobucket then hit reply and bam your photo will upload in the thread!
If you have a smart phone you can get the photobucket APP which will automatically upload every pic you take to photobucket so then you can simply just log on and post your pics quick! Hope that helped, being able to post pics of your truck/work is a big deal!