How to decide which hand is the strongest?

Question

I am working on a Poker Calculator.

Can someone give some guidelines or some good resources on how to decide which hand is the strongest?

What I am referring to is that I need to send in a total of seven cards and figure out which is the best five card hand of those seven cards.

However they are not in order as the cards will be randomized.

So for example I send in these cards:
2s 9d Ac 8c Ah 9s 8d

How can I make so that C# finds out the strongest hand?

/Tomas