Welcome to the forums! 
I use Imgur for hosting my photos.
Here is what I do to add pictures to my posts with Imgur:
1. I login to Imgur and find the picture I want to post:
2. On the Direct Link Option click "Copy".
3. Now go to FSM forum and find the Thread you want to add the picture too.
4. Find the post and click the "Reply" button. (If you do not see a reply button, you may need to refresh the browser screen. Or go to another post that does have a "Reply" Button.) You should see the next picture:
5. The add picture icon is circled in Red. Click on it, the next pic will show you what needs to be added:
6. Source circled in Red is where you will paste the copied information from Imgur, or any hosting site. Then I set dimensions to 500 X 350 and I leave Constrain proportion checked. These are arbitrary numbers, they can be set to whatever your prference may be. I do not add an Image Description, however you can if you like.
7. Click "OK" to add the picture. At this time you still have not posted the post, and you can go back and make adjustments. When done, click on "Submit your reply" at the bottom of the page.
8. Hope this helps.