Pick a number 1-100 if you win you get a Playblink invite

This is the answer to everything.

They do. Copy pasting from the website (can screenshot if needed just bored) :

This page allows you to view your referral history. You can earn charity points by inviting your friends to PlayBlink. You will receive 5% Charity Points of your friend's initial donation and 5 Free Points for each referral, plus achievement rewards as listed here. If you wish to invite a friend, please give him/her an invite code listed here.

It is really, no other way of looking at at I suppose :(

Playblink call it a "referral program". You get 5 points for everyone you invite, plus 5% credit for their donations for entering giveaways.

You're talking to the head mod of steamgifts...