On the top left hand corner of your screen, top on your profile picture, then tap Settings

Tap on the tile with your name and profile picture

Here, you can edit your name, profile picture and create a username

Go back to the settings page, and tap on Account

You should see this screen. Here, you can create a PIN and set a Registration Lock. You can also download and export your account data and delete your account from here

Go back to the Settings page and click Chats

You should see this screen. Here, you can limit access to your device contacts and delete your chat history

Go back to the Settings page and click Notifications

You should see this screen. Here, you can limit the content within a notification to show "Name, Contact, and Actions," "Name Only," or "No Name or Content"

Go back to the Settings page and click Privacy. You should see this screen.

Tap Phone Number at the top of the screen. Here, you can adjust who can see and find you on the Signal app via your phone number

Go back to the previous screen. Here, you can update additional settings, such as setting a default for disappearing messages and enabling app security, including when to lock access when leaving the Signal app

Signal Hardening Guide