Proxies basically are another ip address, since instagram will see if you have like 10 accounts all running at the same time under 1 ip, it's a bit suspicious.
So you get proxies, and make it look like just another normal user instead of a spammer.
Best to use 1-3 accounts per proxy, technically you can run 5 accounts without a proxy but just to be safe, i'd recommend you get some.
Lots of quality sellers in Marketplace to your left <---
I personally use SSLprivateproxies and i like their quality and support.