Save attachment you received
In the message, touch & hold the attachment, then touch   > Save. Or, touch the attachment to open it and 
look for save options.
If you don't save an attached photo or video, it is kept within the message only. So, if you delete the 
message, you also delete the attachment. (You can try to recover recently deleted messages.)
View saved attachments
For photos or videos, open the Photos app and touch Library.
For other attachments, open the Files app.
Use apps : Text messaging 106