Every sentence must have end punctuation and must be have the first letter of its opening word in caps, unless you happen to be  e. e. cummings .(He was able to do such things under the protection of his  poetic license . However, you first need to know and be able to utilize all the rules before you can break them!) 

• as the first letter of a new sentence
• for proper nouns
• For the first letter of the first word inside a direct quotation