Reading, Spelling etc. all helps besides the games one plays.

Correct pronounciation refers to the way the word should be said within a language.
Unfortunately some people use slang and whilst may be totally acceptable in private discussions, it is not acceptable in many parts of the business world and certainly not in letters etc.

Texting which abbreviates many word e.g. c u (meaning see you etc) is OK but good accurate wording of letters, documents that are not ambiguous can be vitally important.