Is One Time Pad something like this? Alphabet: [A-Z] = [0-25]

Plaintext = HELLO = 7 4 11 11 14

// QUESTION: do this key must be as long as plaintext?

KEY: [QWERT]
KEY = 16 23 4 17 19

Plaintext + Key = 23 27 15 28 33

Plaintext + Key (mod 26) = 23 1 15 2 7

Cyphertext: XBPCH

So is it correct that IF plaintext = "HELLO!" THEN the key must be six characters long, such as "QWERTY"?
For the one time pad, your key must be


The same length as the message. Whatever your unit of measurement (bits, bytes, etc), they must be the same length.
The key must be perfectly random.
The key is only ever used once.