Here's how
1. Go to the windows start button in the bottom left corner of your screen/keyboard, Type in "%appdata%, Click on the "Roaming" file, Go to the .minecraft folder, Go to "screenshots"
2. Locate screenshot.
3. Go to imgur.com, In the top right of your screen, you'll see "upload images," click on the "computer" tab under that, If needed, type in %appdata% again in the "file name" slot, Click .minecraft, Go to screenshots, find screenshot, double click screenshot.
4. Click the "upload" tab. (If you want to edit the image, check off the "edit" box.)
4a. (If you want to edit the image, follow these instructions. If not, skip to step) Edit the image however you want, click the "save" tab.
5. You will see a bunch of links on the right of the page. Easiest way is to highlight then copy (Press on keyboard "ctrl+c") the link called "BBCode (message boards & forums)", then come back here and do ctrl+v on the keyboard wherever you want to paste the link. (If you wanna see if it worked before you post the screenshots. Press the "preview" tab next to the "post" tab, if you like how it looks, press "post."
(Non-BBcode method of posting screenshots): Do steps; #1.-2. (Say you are using another site than imgur, click whatever tab says upload image, go to the %appdata% file, .minecraft, screenshots, double click screenshot.
Upload it, right click on image, in the menu that pops up, click "view image", if you are brought to a page with the image in the middle and a gray background surrounding it. You've done well. highlight and copy the url link.
Come back here, look for the tab that say "insert image" when you hover your cursor over it. (In section that let's you modify what you have typed.) "
" will appear, inside them "
", paste the link you copied earlier. Press the preview tab to check if it worked.
If I messed up, tell me where your stuck at, I was kinda just rushing through. I'll tell you what to do if you messed up then.