iOS 8 has made group messages friendlier and manageable by adding some important features. Though not much different from iOS 7, you have more options (most notably, leaving a group message or muting it).
If you're new to iOS or if you'd like to just know how to start a group chat in the Messages app, here's how to do that easily. Note that you'll need to be running iOS 8. Also, group messages work for iMessage.
How to Start a Group Message on iOS 8 on iPhone and iPad
Step #1. Open Message.
Step #2. Tap on the Compose New Message icon.
Step #3. Type the email-id or phone numbers to the people you want to send the message.
Step #4. Type the Message you want to sent.
Step #5. Tap on Send.
That's it! You have sent a group message.
It's a group message because whenever someone replies to this message you sent, it will show up on the same screen as a thread. When all the others respond, you won't get individual messages: instead, all of it appears on this thread.
If you have a lot of group messages going on, you'll pretty soon find out that the conversation list can be very congested. Naming each group can help you quickly figure out who you are talking to. Here's how to do it:
Step #1. Open the group message.
Step #2. Tap on Details (top-right.)
Step #3. Swipe/drag the screen down and type a name (for the group) in the Group Name text-field.
How to Add More People to the Group Message in iOS 8?
If you want to add a new participant/recipient to the group message, you can do that too! Here's how:
Step #1. Tap on Details.
Step #2. Tap on Add Contacts.
Step #3. Add the phone numbers or email-id you want to include in the group.
The new member will be added to your group and will start receiving messages you send in the group.