You can use the glue straight or dilute. I prefer to add a bit of water.
I smooth the glue with my finger or my hand. I keep a wet cloth near
me so I don't have to wash my hands every time.
Wrinkles - It's important to stabilize the batting before putting the top
or backing. I use those big clips as I baste on a big board.
I would definitely not add the glue like in the video. It leaves too much
big gaps. I prefer to "write" with the tip of the glue. Make small waves
and close to each other...that sort of mimicks pin basting.
I don't know why she uses a water bottle. I've never used one.
Totally unnecessary in my opinion.
If you baste in sections on a table, specially when working on a big quilt,
make sure not to leave any big gaps between the last line of basting.
Start close to where you left.
Hope this helps.