Via Your Phone's Contacts List (Most Common & Reliable):
Save the Number: First, ensure the person's phone number is saved in your device's native phone contacts (e.g., your iPhone Contacts app or Android Contacts app). Make sure to include the correct international country code (e.g., +880 for Bangladesh).
Enable Telegram Contact Sync (if not already):
Open Telegram.
Go to Settings > Privacy and Security > Contacts.
Ensure "Sync Contacts" is toggled ON. (You can toggle it off later if you prefer, but it helps find contacts already on Telegram).
Check Telegram's Contacts Tab:
Go to the "Contacts" tab within Telegram.
Telegram automatically checks your synced telegram number database contacts against its user base. If the person is on Telegram and their privacy settings allow you to find them, they should appear in your Telegram contact list.
You can then tap on their name to start a chat.
Manually Adding as a New Telegram Contact:
Open Telegram.
Go to the "Contacts" tab.
Tap the "+" icon (usually in the bottom right on Android, top right on iOS, or "New Contact" option on Desktop).
Enter their First Name, Last Name (optional), and Phone Number (including country code).
Tap "Create" or "Done".
If they are on Telegram and their privacy settings allow you to find them, their Telegram profile will appear, and they will be added to your Telegram contacts. If they are not on Telegram, you will typically see an option to invite them.