Copy the FEN string next to the move list on the game (this is only necessary if you want the line to have a starting position as the current position of the game):
Then click on the little board icon above the comment box:
Select the second option, "Game or sequence of moves," click "Continue," select the second option to input an FEN string and paste the FEN string that you copied before:
Click "Continue," then "Enter Moves." Enter your moves, and insert the board into your comment!
It's as simple as that! There are other features and options that you can explore to make it fancy, but it's not necessary and you can just ignore the other stuff if you want. But if you're like me...you'll probably enjoy exploring it a bit. :)
How to post a line on a board...
Copy the FEN string next to the move list on the game (this is only necessary if you want the line to have a starting position as the current position of the game):
Then click on the little board icon above the comment box:
Select the second option, "Game or sequence of moves," click "Continue," select the second option to input an FEN string and paste the FEN string that you copied before:
Click "Continue," then "Enter Moves." Enter your moves, and insert the board into your comment!
It's as simple as that!