No problem. Having worked with the Hirst stuff there's a bit more advice if you want better castings. I'm no expert but this is what worked for me after hundreds of castings. I watched a lot of youtube videos to see how other people did it and borrowed their techniques.

You can mix the stuff using the plastic cup method on Bruce's site. Just measure out what you need in a cup and nest one cup in the other and using a drawn line you can approximate. I got much much better results after switching over to using a medical irrigation syringe, some measuring cups, and cheap 10 dollar scale to weigh out my stuff. If you've weighed things out a few times you'll get a good feel for how much to use but at first I would stick with the calculations for the volume and weigh your stuff otherwise you'll waste a lot of time doing trial and error.

Don't try and be stingy with the hydrostone and pour short or try and scrape up anything that has spilled over into your tray. It's so easy to want to try and save everything and not waste, but anything that has run off is going to be loaded with water. This causes an incorrect ratio and the when you scrape can get extremely soft and break if you don't scrape and pour right.

I had cast lots of bricks trying to get every last bit of plaster and ended up having to throw out those bricks as they ended up the wrong size or broke too easily. They were still useful for broken rubble or whatever but totally avoidable.

Some people like to wait until the plaster settles and then soak up water with paper towels or something and that never worked right for me. The bottoms or sides of the bricks ended up with a weird texture from the paper towels. Scraping flat with a very good quality drywall knife/putty knife is the best bet and just leaving it be.

Wait until it's like toothpaste(just give it a poke with your finger and then scrape flat. Any later and you won't be able to scrape and have to use more pressure and may break. Too early and your bricks will come up short as the water didn't rise to the top completely.

A cheap plastic knife will work ok, metal is better, but get one that is wider than the molds so you can do it in one pass and not gouge the bottoms of the bricks. Use very light pressure when scraping so you don't pull the silicone away and cause the bricks to break or deform before they are dry.

When you think the bricks are hard and read to take out, they're not. Some thick bricks can be popped out early with no problems but some thin pieces will ALWAYS break unless they have cured for awhile. I'm looking at you stupid metal gates and doors or columns.

After you demold, put them on a tray and bake them in the oven for a few hours at around 200F temperature to cure them and make them rock hard. If you don't, the moisture will not leave the bricks completely and they can remain soft for some time. Leaving them out for a few days or week will cure them also, but oven speeds up the process considerably and is 100%.

I hope you read up on Bruce's site about how to do the jet dry wetter water trick. It helps a lot. I've also strapped a back masager down to a folding card table with a truck tie down and put a board with sponges on the bottoms on top to hold my tray. The vibration gets rid of a lot of those pesky bubbles and helps plaster flow better into those smaller bits and hard to reach places. You may get frustrated with the quality of your bits without the water bath and vibrating table since they'll have pock marks and divots in them or sometimes a piece may cast only 50% like small barrels.

Let me know if you have any further questions. I hope this all helps you avoid a lot of the issues I had but you'll probably still mess up your first few castings because I did even after researching and reading everything so don't sweat that.

Good luck.