There are 2 image icons above your reply/text box.
If you wish to host an image on this site, click the icon on the left, hit browse, locate your image in your files and select. Then hit 'host it'
You will get 3 links, select the middle one by clicking copy ( you may have to select 'allow' )
Then simply paste into your text box.
If you are posting an image featured elsewhere on the net, right click on the image, click properties, highlight and copy the URL.
Select the image icon on the right and paste the URL.