EDIT: Please also read the comments, especially danzo321 has written really good advices, since I'm not an expert but sharing my experience reading the comments would make your process easier =)
This time I am going to show you how to take an alginate mold of a face (and fill it with plaster)
What you need,
A model ;)
Several cups (to mix, pour water etc)
A pillow (you have to make the model comfortable =)))
Small pieces of paper (or you can use straws, I didn't have any so I used paper)
Mix your alginate with water
Now if you have people around you make them help you =) It would be much quicker if someone else also mixed alginate with water in another cup so you guys can pour it together. I had only one extra so I made her take the pictures and did all the mixing myself.
If there isn't someone to help, be patient, don't try to mix huge amounts of alginate cause they are going to dry quick and you probably will waste a lot of alginate.
REMEMBER! If alginate is getting light pink it means you only have a few seconds to pour it on the face. Best to use it while it is dark pink/purple.