Co-Op Confusion - Help Please

Hello,
I was just wondering if someone could help me? I have searched the internet many times and cannot find the answers I'm looking for. A friend of mine has Dark Souls and tells me it is one of the best games he has ever played, and also told me co-op was more or less being paired with a random person. The question I would like to know the answer to is:

Since the new DLC and Co-Op matchmaking feature can you invite friends and play with them?

As the DLC states Co-Op matchmaking, as I have mentioned I have looked everywhere and no one can give me a definitive answer to my question.

Can I invite a friend and play Co-Op with them?

I am a 360 user by the way and will buy Dark Souls if this is possible as I play most of my games Co-Op with said friend. Many Thanks in advance to anyone who can tell me this simple yet difficult to find answer.

I look forward to hearing from you. Many Thanks

You cannot invite friends to just join your world.
Whoever wants to be summoned has to place a White Sign down through a White Soap Stone. Most people will be able to see it and they might summon you instead of your friend. You could set a point for the sign such as in a barrel where your friend will know that it's there, when other players will not.

Thank you for taking the time to reply. That makes total sense, and is just as good as being able to invite a friend. I will be a noob to Dark Souls in the next couple of days.

Again Thank You