You can mix and match the armors as you see fit, but some weapons require the full set of armor to function properly, such as the Tank job's shells. Without the armor, the weapon does nothing.
You might be wondering how to become the job/role? You'll need to craft the Antique Charm; a mysterious necklace that lets you become the job of your choice. You can craft it using 2 leads and an ender pearl.
In the original game of Miitopia, there's 14 jobs, or roles you can choose. Each one is different than the other. I'll show a few of them:
Warrior- 
Warriors are great for doing some damage and taking some damage for friends. The squire sword is slightly stronger than a diamond sword, making it a great weapon choice! Take down undead monsters easier with the Undead Slash ability and take less damage with Proud Protector!
Mage- 
What's an RPG without a mage class? Mages specialize in doing magic damage with fire and lightning. Don't bother trying to attack with your wand, it won't do much damage. Keep an eye on your MP (appears on the bottom left on your screen). Without enough MP, you can't use magic attacks! The armor doesn't have too much defense, but it makes up for it with high enchantability.
Cleric- 
Every team needs to have a healer! The cleric specializes in healing and removing negative effects on friends.
They can heal teammates with the staff's projectile (and themselves by aiming upwards). It's especially effective against undead monsters. Don't forget your book, you can try to instantly kill monsters by right-clicking them with it. (You'll also need to watch your MP numbers!)
Chef- 
Here's an interesting role; the Chef. They can cook up a storm with their frying pans (provided you have raw meat in your inventory). Chefs can take even less damage than Warriors making them more durable in combat. Try out the flambe ability. You can set enemies on fire with it, or you could try to literally make a meal out of monsters by cooking them. They have the defense, but not as high enchantability.
All jobs come with a special ability that may require you to have a specific item in your main hand. I'll go over a few There's way too many to put here.
Book: Imp and Cleric Job
Light-blue dye and Purple dye: Vampire job
Lime dye: Mage Job
These items serve as ways to use magic abilities the Job provides.
Also, don't forget to make HP bananas! They're essential for your survival! If your health is too low, you can eat one of these to heal yourself! MP candies are important too. you'll be able to increase the amount of MP you have:
Mobs:
Two more things before you go: To reset your job, make the Job resetter with 3 Light blue dye, a book and red dye. Just be aware that your inventory will be cleared when doing this! (It's meant to get rid of the old job items)
And download JEI (Just enough items) if you don't know how to make something!
The great sage-
If anyone's played the actual game, then you'll know that this person plays a big role in Miitopia (no spoilers).
You can find her roaming around your world from time to time. She'll have a glowing effect for a few seconds when she spawns in. Interact with her to get items like MP Candies or an emerald.
On occasion, she might just disappear without even giving you anything!
Fiend- These flying menaces spawn on Hard Difficulty, and only on Hard for one reason; They can one-shot you! I recommend shooting them with projectiles or a heavy hitting weapon to defeat them. Or, have the Absorption effect to take a hit. Are you brave enough?
