In the time of the Caesars a code method was developed. It became known as the Caesar Cipher.
The Cipher used the idea of an Alphabet shift. Say, using the English alphabet we shift 1 this means that a is now b and b is now c, and so on.
A Vigenère Cipher uses the same idea as a Caesar Cipher but instead of a standard shift it uses a keyword shift.
For example; If I want to send the word "hello" as a Vigenère Cipher I might choose a Keyword like dog as my shift. D - is letter 3, O - is letter 14, G - is letter 6. This means that I will rotate the shifts by 3, 14, 6. So "hello" is shifted like this;
| normal text | h | e | l | l | o |
| SHIFT (Keyword DOG) | D-3 | O-14 | G-6 | D-3 | O-14 |
| Coded text | h+3=k | e+14=s | l+6=r | l+3=o | o+14=c |
Thus the coded "hello" text becomes ksroc. As you can see this is a very powerful cipher. Even the two 'l's in the middle of hello don't look like doubles!
The longer your keyword is the more combinations there are to decode - this is quite a hard cipher to crack but computers can crack it.
The One-Time Pad is a more complicated version of the Vigenère Cipher. Essentially the length of the keyword matches the length of the message. Generally also the keyword is not a keyword at all but a random generated set of numbers used to shift each letter in a random way. As with all SHIFTS, KEYWORDS, or RANDOM KEYS they need to be communicated to the correct recipient of the message to be used to decode the message and this presents other problems.
Asymmetrical Encryption is what HTTPS does when you request a webpage. It shares a public key to create a connection and then communication progresses using a private key.