co-location

What are the advantages of co-location usage? What does one have to start from?

Sorry but i've never heard of 'co-location'. What is it exactly?

If am to understand right it is being hosted somewhere that other companies are hosted?
If so, I see no benefits.
If you are talking about chain-companies, then there would be benefits as each company would promote the other.

I guess there are advantages of collocation, but they work only if you have enough of initial investments and lots of commercila projects, so this will be good company. Still dedicated hosting is a headache free solution in the most of cases.
Anyway, if you are looking for colo hosting provider, prioritycolo.com, serverpoint.com, hqhost.net might be good options.

Tankara, one has to start from purchasing servers, say from Cisco and then proceed to finding a colo services provider in the area he has chosen, say serverpoint.com offer colo services in Las Vegas. One more aspect if your provider datacenter is low-density or high-density if that's important for you.

What do you mean saying low-density and high-density? Are you talking about the network or what?
Co-location business isn't an easy and cheap thing. You must have enough finance to run it.
Let's take ServerPoint.com, they provide this business for a long while but they haven't started from it. They have earned money for that and then began to provide co-location. Many conditions must be taken into consideration before starting this kind of web hosting services.