What happens when you order
You put your link in the box and press the button. The next screen opens with it already filled in. You choose how many subscribers you want, pay, and the order starts after that.
Where to find it
Your handle is under your channel name. A full youtube.com/channel/... link works too.
Check this first
Only Public and Unlisted uploads can be reached. A Private video is locked to everyone except you.
Why order YouTube subscribers
A stranger who lands on your channel checks the subscriber number before almost anything else. Worth knowing: getting into the YouTube Partner Program also needs real watch hours, so subscribers alone won't unlock monetisation.