When you click on an available lot, you will be presented with a window similar to the one shown in the image below. The "Add to Bulk Draw" button will be in the bottom left area, as highlighted in the image.
Once you add the lot to a Bulk LotDraw, you will see a notification at the top of the screen that it has been added, as shown below. You can continue adding lots to the Bulk LotDraw simply by clicking on them. As you add lots, you will see the number of lots in the notification bar change as well as black outlines around the lots that have been added.
To submit the Bulk LotDraw and start the agreement generation process, simply click submit. More information on Bulk LotDraws can be found here: How do I perform a Bulk Lot Draw?