Lots of people are reblogging that armour gif again saying they’re happy to know the names of the various parts, so here’s a few more diagrams. Naturally, some styles of armour have extra or different parts and there are specially made suits for jousting and such.
A really important thing to note is that not every soldier/warrior of the time had plate armour. Chainmail was much more common. For as cheap and available as it was, it did a great job against most bladed weapons. It was only when swords made for stabbing and advancements in arrows came about that could break through the links that plate armour started to really get going. But it’s expensive and has to be custom made for each warrior, unlike the one-size-fits-all chainmail tunics.
The main thing to keep in mind when designing armour is what purpose you want it to serve. Does your character need maximum mobility? How do they fight? Do they come from a background where they could get their hands on a fitting suit? And if they are wearing a full suit of armour, make bloody well sure they can move in it! Fantasy armour is more often than not, impractical and does not “meld” together. Ever play a video game and your character’s armour will clip through their own body? Yeah, don’t do that. You’ll feel like a master if you come up with armour that fits well.