It's not all that complicated. What you need is an account with a free image hosting site. There are a few that all work similarly, but I'll use Photobucket ( at
https://www.photobucket.com ) as an example here.
You open a personal account by registering with a user name and a password. Then you can upload pics from your own hard drive into "albums". For each pic you have in an album, you get four options for "sharing" (down at the right). These are just different ways of coding the pic's location on the web for different purposes.
To put a pic into a post on a forum such as this, choose the 4th or lowest option. Just click on the address (it will begin with [IMG] ) to copy it into your computer's clipboard memory. Then (assuming you use Windows) paste it into your post where you want it to appear by using either "Edit > Paste" on the browser menu, or the Ctrl-V key combo.
That's all. You can check that the pic appears as you intended by using the "Preview" option before sending off the post.