Grammar is important for classroom assignments, being professional, and everyday communication. Proper use of commas includes listing commas, joining commas, gapping commas, bracketing commas, interjecting commas, and speech commas. Common grammar mistakes include confusing its/it's, your/you're, their/there/they're, who's/whose, then/than, lose/loose, alot/a lot, and definitely/definitly. Capitalization rules include capitalizing the first and last words of titles, names of days but not seasons, and the first word of salutations and complimentary closes.