Do I use all my messages in the secure compose now, or can I use the other compose as well? I'm unsure how the encryption works. Do I need to tell my friends to get the encryption thing too? Or does this encrypt all messages to and from people either way?
For each message, you get to choose if you want it encrypted or not. If you want the message encrypted, use Secure Compose, otherwise use the normal one.
You can send an encrypted message to anyone, but it's more convenient if the other side has encryption set up as well, because if they don't, you'll need to add a password to protect the message with, and the other person needs that password to open that message - that's too cumbersome for normal communication, but appropriate if you need to send something sensitive.
What I do is this: