To get your roll to post in the appropriate thread, follow your GM's instructions on where the dice roller posts should go. I usually put mine in a separate thread from the game or out of character posts so it doesn't get cluttered up, and you have a list of rolls to go back through in case of any disputes.
To get the URL or page address you need to post your rolls in, go to the indicated thread and click the Reply button for that page just like you were going to respond to a message there. Then, instead of typing a response, go up to the adress bar of your internet browser and copy the address, just right click it and it usually gets hilighted and a pop up menu will appear. Click copy, and you've got the address needed for the dice roller.
Open Konkret Dice Roller, and click the "Forum Post" button. At the bottom of the roller's interface, a new text area will appear. It will say, "Post the results to Roleplayers Direct by using this 'reply' link:", followed by another text entry area below it with the message "Enter a link here...". Right click in that text area and the pop up menu will appear again. Click "Paste", and the address you copied in the Reply page address bar will appear there. Once you've set up your roll with the proper dice and amount to roll, then click the "Post" button on the bottom right of the program window. Your roll will then be posted as a reply to the indicated thread.