1) Find an image you like. If using Google image search, make sure you've opened the image in it's own tab as shown:
2) Right click the image and select 'Copy image address' (works in Chrome):
3) To insert into a post, first hit reply:
4) Then hit the little picture icon as shown:
5) This puts image tags into your post:
6) Put your cursor in the middle of the two tags and right click, paste the copied image link:
7) Hit post. You're done.
8) Once you become pro, you can just type [img][/img] into the quick reply box and paste in the link avoiding steps 3) to 7).