It's way easy. Collect the pollin (if you intend on saving it in the freezer, use the proper container)
Pull the plants you intend to pollinate out of the flower room. Shut off ac, in house, warehouse, or whatever your grow spot is, al well as carbon filters, and fans in grow room. If you have a good negative pressure, and any pollin spills, it can be sucked in your flower area, and expect a whole lots beans, so cutting off anything that circulates air is important.
Once you have everything set, use a wet paint brush, and pollinate all the branches you want done. I like to put a twist tie, and label each branch with what pollin was used.
Let it chill for a few, and put it back in.
The pistols will begin to recede, and you'll have pleanty of beans, and you'll know what cross went to what branch.
You have pleanty of good advice from just about every post I read. It's not rocket science yet, just be cautious, and use common sense