Take a Screenshot - While in FSX you can take a screenshot by pressing the "V" key. The game may stop for a moment or not. There will not be any notification that you took a picture, Take as many as you want and when you are done, exit FSX.
Hint: Press "shift + Z" to display the current coordinates which is useful when posting a support screenshot.
Find your Screenshot - You will find your screenshots in a folder called "Flight Simulator X Files", This is located in "Pictures". Go into the folder and you will see all of the screenshots you have taken within the game. Decide which one(s) you want to post.
Edit your Screenshot - This is mainly an optional step. Some people use editing software such as GIMP or Photoshop to add effects to their screenshots and/or edit the colors to make them look better. You will want to change the picture to a smaller file size, By default FSX saves the picture as a .BMP, which is a very large picture file. We want to make it take up less space and be easy to upload, so we should change them to a smaller file such as a .JPG (JPEG). To do this, right click on the picture of your choice and then click "Edit". This will open up paint. Go to File>Save as..., and in the drop-down box pick .JPG. If you like, rename the picture in the box. Then, click save. Exit out of paint. Now, you will have two copies of your screenshot, one saved as a BMP and one as a JPG. Delete the BMP copy as you don't need it anymore.
Upload your Screenshot - Now you need to upload the screenshot to the internet and make it a viewable link. To do this use a website that will save your picture as a link, here are a few suggestions (you only need to use 1 of them)
http://fsfiles.org/flightsimshotsv2 - You want the link that is called "BBCode"
http://imageshack.us/ - You want the link that is called "Forum"
http://postimage.org/ - You want the link that is called "Hotlink for Forums (1)"
http://tinypic.com/ - You want the link that is called "IMG Code for Forums"
http://photobucket.com/ - You want the link that is called "IMG"
Once you have your link go to the topic that you want to post the screenshot in. Move your cursor to where you want your screenshot to be and hit paste, don't forget to add any comments to the post.