Enter their Mobile Number, including the correct country code.
Tap "Create" or "Done".
If the number is registered on Telegram, their profile will appear, and you can start chatting. If not, you'll be given an option to invite them.
Why it's good: Convenient if you already have their number.
Privacy consideration: When adding by phone number, be aware of your "Who can see my phone number?" and "Who can find me by my number?" settings. By default, if you add someone by their number, they might be able to see your number if your settings allow it for "My Contacts."
3. Adding from a Group Chat
If you're in a common group with someone, you can add them directly from there.
How to do it:
Open the group chat.
Tap on the group name at the top to see the list of members.
Find the person you want to add and tap telegram number database on their name/profile picture.
This will open their profile. You can then tap "Message" to start a chat, or if the option is available, tap "Add to Contacts" to formally add them.
4. Using a QR Code
Telegram allows you to generate a QR code for your profile, and you can scan others' QR codes to add them.
Open Telegram.
Go to Settings.
Next to your profile picture, you should see a QR code icon (it might be small or require tapping your profile to see it).