The pictures need to be hosted on the internet upon another site, such as a blog or photobucket.
Once the pictures are up on the internet you require the URL image data - this is achieved by right clicking [on a mouse or keyboard scrollpad] upon the picture you want to use and selecting "Copy image URL".
Once you've got that information (which is kept hidden and in your computers memory) you come over to this forum and create a new post/reply to a post and select the "image" button from the control panel above where you type your post (the image button looks like a pictureframe with mountains and a sun inside).
When you've clicked the image button a pop-up box will appear on your screen and it will ask for the URL you wish to use - this is where you paste the URL data you copied earlier. To do this, right click on the URL entry and then select "paste" from the menu that will appear. Your image may or may not appear below, inside the pop-up box.
Press the green button on the pop-up box; "okay". Your image should now appear in your draft post ready to use.
It sounds complicated, but it isn't. Once you've done it a few times it's easy.