I've used it on small baby quilts. I lay the backing on the floor wrong side up. I stand holding the glue bottle and bend over until I can let the glue run out in a steady stream with no lumping. The hard part for me is keeping pressure on the bottle so that I get a long thin line from top to bottom of backing. I do about 3 rows for the crib size. Then I place the batting on and smooth it out. Let dry. Then repeat for the batting laying the top onto the glued batting and smoothing it out.
I try not to get glue too close to the edges.
If you're like me, you'll definitely get glue on the floor. I have laminated flooring and the glue cleans up easily. I just use a damp mop. If it's on the floor too long, it may require getting on your knees with a bucket to get it off. I've been there too.
A quilter told me that she pins the backing to her design wall and dribbles the glue onto it. I think that would be manageable but a lot harder to do.
There are threads about this topic here on the board. Type Elmer's Glue into the search box.