The dahs (or dashes) should be three times longer than the dits (or dots).
The time period between characters should be three times longer than the period between the dit/dah elements within a character.
The time period between words should be three times longer that the period between characters.
The bar over multiple letters in the Special Characters section indicate that they should be sent continuously, as if they were all a single character.
A Short (and Very Incomplete) History of the Morse Code
The Morse Code began its development roughly in 1836, when Samuel F. B. Morse, Joseph Henry, and Alfred Vail developed an electrical telegraph system. A code was needed to transmit messages, using only the electrical pulses the telegraph could send and the pauses between them.
In 1837, William Cooke and Charles Wheatstone in England developed an alternative telegraph system using pointing needles that rotated above alphabetical charts to indicate the letters that were being sent. However, the inventors failed to find customers for their system.
The Morse/Henry/Vail telegraph was originally designed to make indentations on a paper tape when electric currents were received, and the Morse code was developed so operators could translate the indentations into text. Morse had planned to transmit only numerals, and to use a codebook to look up each word according to the number which had been sent. However, the code was soon expanded by Alfred Vail to include letters and special characters, so it could be used more generally. Operators later learned that they could translate the clicks directly into dots and dashes, and write these down by hand, thus making the paper tape unnecessary; and that people become more proficient at receiving Morse code when it is taught as a language that is heard, instead of one read from a page.
Morse Code began to be used extensively for radio communications in the 1890s. Beginning in the 1930s, both civilian and military pilots were required to be able to use Morse code. Morse code was used as an international standard for maritime distress until 1999, when it was replaced by the Global Maritime Distress Safety System. When the French Navy ceased using Morse code on January 31, 1997, the final message transmitted was "Calling all. This is our last cry before our eternal silence." In the U.S. the final commercial Morse code transmission was on July 12, 1999, signing off with Samuel Morse's original 1844 message, "What hath God wrought", and the prosign "SK".
Multiple versions of the code have been created over the years, including Morse's original version, a continental (Gerke) version, and the current International version shown above, as adopted by the ITU. Gerke's version, created in 1848, changed nearly half of the alphabet and all of the numerals, resulting substantially in the modern form of the code. After some minor changes, the International Morse Code was standardized at the International Telegraphy Congress in 1865 in Paris, and was later made the standard by the International Telecommunication Union (ITU).
More information is available on Wikipedia.
Here's a link to an interesting article from the IEEE on some competitors and predecessors to the Morse Code:
Morse Code’s Vanquished Competitor: The Dial Telegraph
Learning Morse Code
There are numerous methods advocated for learning Morse Code, if you're interested. Many of them are on the internet, often with step-by-step lessons. You will need to select the method that works best for you. Below is a link to one that has been recommended to us.
* K6RAU Morse Code Course
The course is for those not knowing a dit from a dah, first introducing the individual to learn code by sound and progresses in 12 lessons to 5 words per minute. This course was developed before the current international phonetic alphabet was adopted, but it's still a valid method.