I have a 200 Amp main breaker panel and need to install a subpanel.

It's best to install a 100 amp, 2 pole breaker with wire that is rated for 100 amps+ and then bring over 4 wires: The two hot wires, the ground and the neutral to your new 100-amp load center. Be sure to buy the exact breaker brand as your main panel. However, you can use any brand for sub-feed panel -- just maintain breaker types. (If your main is GE, use GE breakers. If your sub-feed is Siemens, use Siemens breakers.)

Here is a video that might be helpful - https://www.youtube.com/watch?v=dppRHWC0x4E

I do not know where you live but unless you are a licensed electrician I would not do this work. Too much risk for a fire.

I would not take a risk with electrical work that you are not familar with - call an expert.

http://www.bhg.com/home-improvement/electrical/how-to-install-an-electrical-subpanel/

https://www.youtube.com/watch?v=97V9H8JdTbk

When it comes to connecting to a breaker I believe you need a permit and an electrician needs to sign off before it can be done. If you don't go through the proper channels and there is a fire that destroys the house your insurance won't cover it.

Even if you do the work yourself, you need to pull a permit and have inspected. If anything happens it could void your homeowners policy. Here is a link for your area.

http://sfdbi.org/electrical-code-interpretations-and-guidelines

STOP!... what you are doing.. and back away from the electrical panel !!

contact HomeAdvisor.com or AngiesList.com (free) can recommend a verified Electrician or Electrical Contractor to do the work for you.

This is one of the instances where "if you have to ask the question... you should NOT be doing this yourself".

The safety of your home and the safety of your family is at stake... get it done correctly.