The C, A, B, D, etc. … are the different keys of the harmonicas. @Luke recommends and uses a Key of C harmonica in the Beginner to Boss lessons, so a Harmonica in the Key of C was my first choice to start with. Others are better qualified to expound on this.
welcome at our place! As @burpsan points out, C, Bb, D, etc. are the different keys.
If you are just starting now, get the key of C first. It makes it easier for you to play the recommended tabs here in the BTB course or on other portals.
With a Special 20 you have a good choice. The Hohner Golden Melody is also popular.
But you will quickly find that every harp player has their own preferences for the numerous models. You will always find a “better” one . And as mentioned before, there are models in every key… and then there are special keys and chromatic harps.
To start, buy a harp that is good but not too expensive. In the beginning, your harp will be heavily used. Use the waiting time to find out more about the harp here or on the internet. You will need it!
When you start the game, keep it easy and relaxed, don’t overdo it. Your muscles and breathing have to get used to the game!
Many users are available here for answers to questions or problems. You will already find numerous answers if you use the search function above.
Most teaching on the net is done using a C Harmonica the next choice would be an A Harmonica as a lot of music is played in the key of E. A Harmonica in second position (when sucking) is the key of E. https://www.youtube.com/@TomlinHarmonica
Most of his lessons are in the key of C
as are most of the lessons on Harmonica.com
C is good and any key above D, E, F is slightly higher and B is also high, but G, A are lower in tone, aka longer reeds. Manufacturers usually give the layouts of blues, country, pentatonic, even low bass like harps.
A big choice is wood comb or resin comb, I like both, wood combs fatten up some after your humid breath swells the wood, resin, lips move easier across the comb.