Apostrophes are a little tricky, but worth mastering. Be sure to use apostrophes in words that are formed from two words, where part of one of the words is skipped. For example, can't is a contraction of the words can and not where the n and o in not are skipped, and replaced with an apostrophe. If you don't use the apostrophe in the word can't it means something completely different. Apostrophes are also used when pluralizing single numbers or letters, such as 5's or R's.
Apostrophes have one other very important use.
They are used to show ownership or belonging. Notice the difference in the locations of the apostrophes. Capitalization - Begin the first word of every sentence with a capital letter. Capitalize I when referring to yourself. Begin all names and titles with capital letters.