How do I get network connections for Samsung Galaxy S6?

[AC Question]

This is my first smart phone. Had it less than 2 weeks. All of a sudden I have the following messages- "Mobile network not available" "Your mobile device is not connect to the network" "No network connection"

 

[STARGATE]

Did you turn it off for a minute and than turned it back on to see if that fixed it?
If so and the issue persists, go to settings, mobile networks, network mode.
From there, choose the one that best suits your needs, or automatic if you aren't sure.