Congratulations! You've buckled to the peer pressure of that one paranoid-seeming friend and started using Signal, which is generally regarded as the "gold standard" in mobile-based instant messaging!
HOWEVER
There's still quite a bit to do to really get it set up. This guide will be incomplete because I haven't used one of its newest features yet, Signal Secure Backups. If it's like the rest of the app then it should be pretty straightforward and self-explanatory. This guide is mostly for the people who don't like changing up the defaults, and I will go over what configuration I personally use.
IMPORTANT NOTE: I'm going off of the Android version of Signal, but the iOS version isn't too different. I will go over the differences I do know of as I go along.
First of all, you'll need to know how to get into the Settings menu in the first place. It's just as simple as tapping your own avatar on the top-left corner of the screen, right next to where it says "Signal." Once you're in the Settings menu you will see your own contact information at the top. Go ahead and select your avatar again. That will take you to a menu where you can change your display name for the benefit of contacts not in your contact list on your phone. In here you can also choose your User Name so you can just give that out instead of your phone number. You'll also see another option called "QR code or link." This way you can have anyone you meet also on Signal just scan that QR code.
Let's exit back to the main Signal window for a second and go over what to do if someone shows YOU their Signal QR code. You'll notice a camera icon on the main page. Just select that camera icon and use it to scan their code, then send a message. On their end it'll show the usual "message request" thing on most other messengers, and if it's accepted you'll both see "unverified" at the top of each screen. To remedy this, both of you in that chat will have to verify one another's Safety Number. To do this, you'll click on the other person's avatar on the top of the screen in the chat, then select "View safety number." You'll notice a QR code that says "tap to scan" at its bottom along with a 60 digit number, grouped in 12 groups of 5 digits. You can either scan the other person's QR code and see if it says "Match" or you can manually compare that 60 digit number. Needless to say it's easier to just scan the QR code but if you're on a different platform and you each know it's the other and want to jump messengers, go ahead and compare safety numbers manually. Now exit out of that chat and go back into the main Settings. This is a setup guide, after all.
Let's handle "Chats." I like to make sure "Generate link previews" is deselected because link previews do run the risk of containing malware, zero-click exploits, yadda yadda yadda. I can always copy and paste the link into a browser with strong adblock protection.
Let's go into Notifications. I make sure under "Show" that it says "No name or message" because it's been shown that law enforcement agencies are able to recover Signal messages using that preview data, so "No name or message" means no data to extract from Quick Settings. I also take this time to select unique ringtones and notification tones specifically for Signal.
Go into Privacy. Most important thing first, and this is where the username you set up earlier in this guide comes in handy: You have the option to turn off searching for your phone number or phone number visibility under "Phone number." You'll still need your phone number for your account, but this will turn off who can see it. When you're done with that, stay in Privacy. This is where you can set the Screen Lock on Signal (I usually have it set to 1 hour under "Custom time"). You can also block screenshots in the app, you can make it to where it can ask your phone's default keyboard disable "personalized learning" (you DID switch to a privacy-respecting keyboard first, right?), and if you plan on sending or receiving money within Signal you can set up to where that needs the lockscreen.
While you're in Privacy, look at Advanced. You can determine if you want all of your calls to go through Signal, you can show if you're online or not, and you can determine if you want to allow messages from just anybody. Be very careful with these settings.
And now, Backups. Like I said, I've never used Signal Secure Backups before but from what I've seen of it the setup looks self-explanatory. I'll be focusing on an Android-exclusive option called On-device Backups. It'll ask you to select a folder to store your backups in and then generate a backup code. DO NOT LOSE THIS CODE. Hopefully you've set up a password manager by now, store the code in there. This way if you have to wipe your phone or anything, provided you saved the backups on your computer you can restore your Signal chats.
Select Data and storage. Here you have the option of whether you want media to autodownload or not, I generally don't. I always download it manually. I have Sent media quality set to "High" and Use less data for calls set to "Never."
Under "Payments" you'll see one of the biggest failures of Signal creator and former CEO Moxie Marlinspike, a cryptocurrency known as "MobileCoin." Go ahead and get a good laugh out of it. That's the only reason I brought this up.
Okay, you got your laugh. Time to finish up, especially since current CEO and overall tech badass Meredith Whittaker did nothing to the app but improve it (username implementation was her idea). First you'll want to decide if you want to link your Signal account to a desktop application. I do this only because typing on the computer is much easier for me, but keep in mind other programs can read what you post on Signal this way especially on Windows 11. I've taken precautions with Linux with this.
You may want to change the Appearance a bit. I keep it in Dark mode and I changed the icon to the "darker" Signal one out of personal preference. You can also change the chat background on here, the font size, and what language you're using.
After all of that, you're done. If you like what Signal is doing and you have extra money feel free to throw some of it their way. They are a nonprofit and survive completely off of donations. You can do that by selecting "Donate to Signal" in the Settings, but it's not mandatory.
Your next job: Convince all of your friends to use Signal, too. The more people we get using Signal the more robust the network will be.