Hello Alayna,
Thank you for using Apple Support Communities! I see you have some questions about how the Hide Alerts feature works in Messages on your iPhone. I would be happy to help provide clarification. The following resource provides additional information as to how Hide Alerts works:
Use Messages on your iPhone, iPad, or iPod touch - Apple Support
Specifically, check out this section:
To stop receiving message notifications, you can use Hide Alerts. Go to the conversation that you want to mute, tap , then turn on Hide Alerts and tap Done. When Hide Alerts is on, will appear next to the conversation. This stops notifications only for that message conversation, not your device. You’ll still receive all other messages and see notifications for them on your Lock screen.
You can also hide alerts for all your conversations by turning on Do Not Disturb. Go to Settings and tap Do Not Disturb or Scheduled to set up a specific timeframe. This stops all notifications on your device.
Hide Alerts simply mutes notifications for a conversation. You will still receive new messages with the conversation threads in chronological order. If a conversation is deleted, Hide Alerts will remain active on any new messages received from that contact.
Cheers!