Welcome back. So now how do we handle these images marked with the Reject flag? Personally, I don't like to delete images right away. I prefer to keep them around a little while and revisit my decision. Of course, if the shot is totally useless (too much blur, out of focus, really bad exposure, etc.) I just toss them.
Once that done go and select all the images with the reject flag by pressing Command A (Ctrl A in Windows). Put your cursor on one of the images (not on the frame around it) click and drag all the images and drop them on the Rejects folder. When you do this the following warning will appear (unless you've already checked the do not show box):
Click on the Move button and the image files with be moved into the Rejects folder. Now you can revisit this folder another day with fresh eyes. If it turns out your rejection was too hasty you can move the image back to another folder. If it turns out you really do want to delete the image go ahead.
There are other methods available in Lightroom for deleting rejected images such as the Delete Rejected Photos... command available in the Photo menu. That command automatically filters for the images flagged as rejected and presents you with the choice to remove them from the catalog or delete them from disk.
But I find this a harsh approach. Perhaps you don't and that is what will work for you. As always I recommend you play with some copied images and a test catalog to get used to how these commands work.
Just a reminder, if you have questions feel free to email me at email@example.com or tweet your question with the hashtag #LRSQA. AYVHA8W2HYG4