Okay I know that NEC requires that cable be secured at each box or outlet you enter for a connection. My question is how do you properly use one of the black round plastic things that secure the wiring? Can one be reused when it has been used before? They look like they are just pushed in but I need to use one at the service panel and I want to make sure it is right

I apologize for sounding like an idiot I am used to using the good old fashioned metal ones.

Are you talking about rubber bushings? If you are, yes, you can reuse them. As to securing the cable, it should be secured within 1 foot of where it exits the box with a staple unless it has been fished.

No not rubber, plastic like this.

Read the datasheet for the bushings you have shown.

Black Button™ Plastic Push-In Connectors

Since the cable will be considered as being clamped, the first staple needs to be no farther than 12", otherwise theses are fine to use.