my s3 will not let me turn on my roaming feature. what am I doing wrong

I am a senior who is trying to learn how to use my Galaxy S3.
Sometimes I get a message "That I am not connected to a network" and then a few minutes later the message or call will connect. Am I doing something wrong or is my phone malfunctioning? Sorry I get really frustrated trying to learn how to use this thing :(

Welcome to Android Central! Which carrier do you have? Do you live in an area with good reception, or borderline reception?

Go to Settings>Wireless & Networks>More Settings>Mobile Networks>Network Operators, and make sure you have the correct network selected (i.e., the one from your carrier).