There used to be a yellow mixing tray at the top of the shelves in the dirty shop. Not sure if it is still there. Just add enough water to make the concrete reasonably workable without the mixture getting too wet. I’d recommend watching some youtube videos about mixing concrete.
We should have finishing tools (ex: trowels) in the dirty shop in one of the crates by the drill press.
Above all this, I MUST STRESS, do not rinse anything with concrete on it into the sinks, toilets, anything connected to the plumbing system. The concrete will cure underwater inside the drains and clog the pipes. Scoop excess concrete into a trash bag and scrape the concrete off all the tools and mixing trays as cleanly as possible into the trash. Get a big bucket you can fill up 3/4 the way with water and wash everything in that bucket. Do not empty this bucket into sinks. Give the bucket time for the concrete to settle to the bottom, the water will turn mostly clear. The clear water can be carefully poured off, i’d recommend down at the street just in case. Then the settled concrete at the bottom of the bucket should be scooped into the trash.