How does buying followers/likes/etc work?

On Instagram or Twitter:
I'm not looking for a bot or to buy anything. I was just wondering...how does it work when you buy followers? How does someone deliver them, do they just have thousands of accounts or..? And if so how do they all follow you? By going on each one at a time or is there a way to mass-follow someone? Thanks x

Using imacros you can automate everything. my browser works without me