Please explain proxies and when to use them.

Proxies mask your computer's IP Address (kinda like your home address) from the site that you are visiting. You use them when you want to hid your identity. If you want to make multiple accounts at Hubpages or another site and they don't like that, then after you've spent all your time setting up 5 or 10 accounts they can nuke them all and ruin your work because they see that they all were registered from the same IP address even though the emails used to register were different. So you'd use proxies either directly or through a VPN like HideMyAss in order to mask your doings.

I use it because I always have a need to make google accounts and if I use a proxy I don't have to phone verify in order to make a new one. You need a bunch of them in order to use Scrapebox or else Google sees all the requests from your home IP and they ban it temporarily and Scarpebox gets no data back and thus throws off your research. There are lots of other uses for them.

They're basically for being sneaky...or paranoid. Some people hate the fact that the anyone knows where they are typing from so they always use proxies.

Basically in the context you are talking about, proxies serve as IP addresses from which you can spam backlinks from and not get stopped because you have multiple IP addresses to spam from. If one gets banned, that's fine you have several other proxies to work with and spam with. That's the idea here, spam efficiency.

If you didn't have any proxies and just spammed from your own IP address, you would very quickly get banned from wherever you are posting backlinks and the juicy link juice comes to a halt.

It is useful for scrape box and avoid being ban from google

Yes you must use private proxies, if you're doing bunch of link building work daily on web2.0, social bookmarks, article.....