You can read about custom fields here . If you need this to be an input field, you should add a Persistent field whereas if you are fetching it from another entity, you should use a read-only reference field. 

I think I did something wrong because after add field from page designer customer order line page have error and does showing any thing

Are there steps to add field from page designer?

You can find details here.

Thanks for answers it is really useful.

but now I faced this error when try publish object :

(The custom object cannot be published since it is currently locked by another process or user. Please try again later)

This is usually because you have made a change and the screen needs refreshed or you should exit out and restart the IFS session.  Often when the other user or process lock occurs, it is with your own current session.  As long as you know there is no other user who could be using the field, it is most likely just your session.

Even after publishing, you often have to restart IFS to see the field even with your own login.