I’m new to the music world and I am looking to purchase a harmonica to get started.
What is the difference between C, A, B, D, etc. Style versions of the harmonica. I’m looking at the following on Amazon and see those options.
HOHNER 560PBXC Special 20 Diatonic Harmonica, C-major
Welcome to the forum, @JonaMusic !
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.
Hello @JonaMusic,
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.
Best wishes and a good start to you Astrid 
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
Thank you everyone!
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.
@JonaMusic hi! 
Sorry somehow I missed this. Just wanted to give you a belated welcome to the forum! I agree with what everyone is saying here. C harp is the best to start on FOR SURE!! Rock on. 
Welcome @JonaMusic ! I’m a newbie as well and I’d recommend getting two C harps. A Lee Oskar with recessed reed plates is nice and for under $14 Folkmaster 1072-C
You need to open these guys up and learn about the instrument. And you can try fixes on the cheap Susuki and compare recessed covers to the old style plates on your lips. all IMHO
If you want to learn to play, you can’t beat B to B. It might seem pricey, but it’s a huge value once you see what’s there and where it takes your playing enthusiasm in such a short time.
Hey thanks for the kind words Rich! Glad you’re enjoying the course…
the lowest tone key (not counting some new offers of low E, F, F#) is G and then A, B, C, D, E, F is the highest tone. Also Bflat is a fav of mine as well as Eflat,
But start with C, a table top tuner will tell you what your note is and a pitchpipe will get you to recognize notes so you can play by ear.
@GreenStamps Yeah that’s true the standard keys are from lowest, Key of G, to highest key of F#.
And 100% agree that beginners should always start with key of C!
The Low Tuning commonly go all the way down to Low C. Low C and Low D are both pretty commonly played, even way back in the day.
Sorry for the lateness of my reply, my email is messed up. Okay, I think Now. Yes I bought a low E and a Rocket I think, I would like to buy the others F# and F, but about $100 each, so I’ll wait. Love the low E.
On a side note I found, or actually my wife found at an antique shop an opera type chromatic harp, the wooden comb, has ramp style openings, two rows and these little openings on either side of the top metal piece. The wood stank horribly of old wood, old spit, old tobacco and old whiskey. So I plan on making a new comb for it. If I remember I can take a picture of the pieces.