1 It is to use / apply something to have good mastery of it.
===To have a good command / a good knowledge / good mastery of something is to use / apply it.
2 Proficiency lies in application only.
1 It is to use / apply something to have good mastery of it.
===To have a good command / a good knowledge / good mastery of something is to use / apply it.
2 Proficiency lies in application only.