How to send Gmail and no one can see all recepients?

Open gmail to new message.

In the line where it says "To" look to far right and there is a small v shaped figure. Tap it and you should get a drop down option for "to" "cc" and "bc" you choose "bc" and all messages go out individually with just one persons email address.
Cc is carbon copy and bc is blind copy just as in hard copy letters and messages.