The system is not new and was introduced by Stanislaus Mink von Wennshein (1620 - 1699) and refined by others with the most recent work by Harry Lorayne, author of many popular Memory improvement books.
Here is the table of numbers and how they convert to letters. The conversion is phonetic so you will notice the choice of letters sound roughly similar.
cargo install --git https://github.com/ernestas-poskus/mem100 --force
$ mem1000 - S / Z
1 - T / D / th
2 - N
3 - M
4 - R
5 - L
6 - J / sh / ~ch / ~G
7 - K / C
8 - F / V
9 - B / P
The vowels (a, e, i, o, u) and the letters h, w and y do not have any associated number so they can be used as fillers or "wild cards" to make the words.
The first step in using the Major System is to memorise the substitute letters. This is quite easy:
0 - Zero sounds like s or c. 'o' is the last letter of zero
1 - The letters D and T have one downstroke
2 - The letter N has two downstrokes
3 - The letter M has three downstrokes
4 - The last letter of four is R
5 - The letter L can be thought of as the Roman L meaning 50 or a hand spread with five fingers, the index finger and thumb forming an image.
6 - The letter J is the mirror image of 6
7 - The letter K when seen as a capital contains three number 7s
8 - The letter F when handwritten, has two loops, similar to the number 8.
9 - The letters B and P are mirror imags of 9.
Pending
0 s, z, soft c
6 j, sh, soft ch, dg, soft g
7 k, hard ch, hard g, ng, qu