If it's just dirt, then I'd try some standard deck cleaner that you can get at any big box or local paint store. Just follow the directions on the bottle. Since it's redwood you could also use a wood brightener. Just make sure you test the cleaner/brightener in a conspicuous spot first before cleaning the whole deck with it.

"i also notice cracking, is this because of the water?"

Yes, decks should not get wet under any circumstances other than acts of nature. Tell that jerk to wipe his feet or get off your job site. The last thing you are going to want to do with that brand new Redwood deck is clean it or put any effort into maintenance. If it wasn't for that nail-bending slob your deck would look pristine forever, right?

OK enough sarcasm. The dirt is not a concern; it will wash off with deck cleaner followed by oxalic acid rinse.
Did you hire the same guy to put on the finish? If so, I hope he at least changes his shoes. If not, I hope you have someone in mind who can do the finish from A to Z. They should know the process and how to properly clean & prep the wood. If you are planning on doing the finish yourself, do good research and be prepared for a lot of hard work. Clean the wood to remove the dirt. Don't screw up a job you already paid someone else to do by trying something you are not skilled at.