@Westislandsavage always willing to lend a hand, It would help is we could start somewhere and then step by step get it accomplished. From your message I am assuming this is your first adventure and the person that sold you the boat did not provide any guidance.
I have never rigged a "Sirrus21" but I have rigged a lot of other sloop rigged boats and I suspect we can solve this one as well.
I looked on line for some pictures and it appears the Sirrus 21 uses a Transom rigged boom. Something like these.
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If you can load a few pictures of your boat and the parts it would help... I found these online.
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Pretty much you start at the transom with a line, go up to the boom, back to the transom, around the block back up to the boom, then to the transom and around the block. The sail moves back and forth across the boat and you tighten the sheet as needed. Relatively simple as rigs go.