Is there a way to add new photos into an existing collection even though they are located in a different folder in Lightroom?

Question

I am trying to add my favorite photos  that are currently located in multiple folders in Lightroom into a single Collection and am not able to do so. I also do not understand the concept of a Collection Set, which might be the solution here. Any assistance would be appreciated. Thanks!

Answer 1

A Collection is the way to provide a quick link to any group of images you select. (Maybe ones you want to sent to a printer, or email, etc)
A Collection does not make a second copy of your images. Collections appear like folders, but the thumbnails in a collection are only "links" to your original images.
Any Development edits you do to images from a Collection set will show the edits in the Library grid view.
Collections are great for any projects like a Book, or Slideshow, etc.
To place image links in a Collection:
Method 1)   "easy"
First- (if you have created a collection set by the + on the Collection PANEL HEADER)- Right-click the collection NAME in the Collection Panel and choose "Set as Target Collection".
   This will place a small + sign to the right of the Collection NAME. (you only need to do this once to 'Set as Target')
Next- (In the library grid view, this can be "All" photographs.!!))- Select one or multiple images, Press the "B" key.
    This will (Bounce, Bump, Bag, Bop) selected images into your "Target Collection"
    So if you select ALL your favourites with ALL photographs visible in grid- you can do it with ONE press of the "B" key.
Method 2) "almost as easy"
Select one or multiple images in the Library Grid view.
Position your mouse cursor in the middle of one of the selected images, hold a left-click and drag your images 'onto' the collection NAME.
(Note: this does not work if you drag from the border frame of an image.)