To create a group chat in Facebook Messenger, follow these steps:

1. Open Messenger : Launch the Facebook Messenger app on your phone or open Messenger on your PC.
2. Start a New Message : Tap the "New Message" icon, usually found at the top right corner. It looks like a message bubble with a plus sign.
3. Select "Create a New Group" : Choose the option to create a new group chat.
4. Add Participants : Search for and select the friends you want to include in the group. You can add up to 250 members on mobile or up to 50 on some platforms.
5. Name Your Group : Enter a group name to help identify the chat for all members.
6. Create the Group : Tap "Create" to finalize the group chat.
7. Customize and Start Chatting : You can set a group photo, change group colors, and manage notifications by tapping the group name at the top of the chat. Then start sending messages to everyone in the group

This process works similarly on both mobile devices and PC browsers