1) History of capital and small letters:
Capital letters were the earliest form of writing in ancient alphabets, date back to the 3rd. century BC in Greece.
The different shapes of the lowercase letters developed gradually through transformations of the capital letters by the elimination of a part of the letter (see ‘b’-beta in Greek- from B) or by lengthening a part of it ( see ‘d’ –delta in Greek- from D).
Small letters were used to write faster on papyrus and parchment.
Now capital letters serve several purposes in English. One of the main purposes is that they help us see when a new sentence starts. They also help us see when a word is a name, instead of just an ordinary noun. They can also often help us see when a string of words is the title of a movie or book, and not just a regular sentence.
2) Capital and Small Letters of some languages:
Capital letters or majuscules are the larger of two type faces in a script. In the Roman alphabet they are A, B, C, D, etc. They are also called capitals (caps) or upper case (uppercase). The latter name comes from manual typesetters, who kept them in the upper drawers of a desk or in the upper type case, while keeping the more frequently used minuscule letters in the lower type case. This practice might date back to Johannes Gutenberg.
Capital and minuscule letters are differentiated in the Roman, Greek, Cyrillic, Armenian and Coptic alphabets.
Most writing systems (such as those used in Georgian, Glagolitic, Arabic, Hebrew, and Devanagari) make no distinction between capital and lowercase letters, a system called unicase.
Indeed, even European languages did not make this distinction before about CE 1300; both majuscule and minuscule letters existed, but a given text would use either one or the other.
2) Usage of Capital Letters:
In alphabets with a case distinction, capitals are used for capitalization, acronyms, and emphasis (in some languages).
Capital letters were sometimes used for typographical emphasis in text made on a typewriter. However, long spans of Latin-alphabet text in all upper-case are harder to read because of the absence of the ascenders and descenders found in lower-case letters, which can aid recognition.
With the advent of modern computer editing technology and the Internet, emphasis is usually indicated by use of a single word Capital, italic, or bold font, similar to what has long been common practice in print.
In typesetting, when an acronym or initialism requires a string of upper-case letters, it is frequently set in small capitals, to avoid overemphasizing the word in mostly lower-case running text.
In electronic communications, it is often considered very poor "netiquette" to type in all capitals, because it can be harder to read and because it is seen as tantamount to shouting. Indeed, this is the oft-used name for the practice. Larry Trask states that "It is possible to write an entire word or phrase in capital letters in order to emphasize it", but adds that "On the whole, though, it is preferable to express emphasis, not with capital letters, but with italics."
Capitalization is the writing of a word with its first letter in uppercase and the remaining letters in lowercase. Capitalization rules vary by language and are often quite complex, but in most modern languages that have capitalization, the first word of every sentence is capitalized, as are all proper nouns.
Some languages, such as German, capitalize the first letter of all nouns; this was previously common in English as well.
In some traditional forms of poetry, capitalization has been conventionally used as a marker to indicate the beginning of a line of verse independent of any other grammatical feature.