First, read the original XKCD comic.
This Python script will generate passwords (or rather, pass phrases) such as the one in the comic. They need to be generated with a computer; humans are hopelessly bad at coming up with a random sequence of words.
Invoke it from the command line using the built in help for details:
$ python3 chubs.py -h
Basic usage with default wordlist (Pride and Prejudice, 64 bits of entropy):
$ python3 chubs.py
5715 unique words in 1 files (12.5 bits per word)
Requested 64 bits; these 6 word(s) have 74.9 bits:
french schemes stand viewing henceforth aspect
Using a custom wordlist:
$ curl -o wuthering-heights.txt https://www.gutenberg.org/files/768/768-0.txt
$ python3 chubs.py -w wuthering-heights.txt
7840 unique words in 1 files (12.9 bits per word)
Requested 64 bits; these 5 word(s) have 64.7 bits:
image luxury overflowing wad interview
Asking for a specific amount of entropy (using default wordlist):
$ python3 chubs.py -b 128
Multiple word list files:
$ python3 chubs.py -w file1.txt -w file2.txt
By default, the script uses Jane Austen's Pride and Prejudice from Project Gutenberg as the wordlist, which is automatically downloaded and cached in your system's temporary directory.
You can also specify your own text files using the -w flag. The words will be randomly selected from the set of words in the text files listed on the command line. Pick any text file you like (or files---you can list as many as you like with multiple -w flags).
The numeric parameter you specify is the number of random bits used to create the password. This is a measure of the password strength relative to an attacker that knows how the password was generated, including what word list was used. Any real-world attacker will have to brute-force at least this many bits.