There's a huge amount of information on this topic. Where have you looked so far and what have you found? You have a lot of reading ahead of you.
YouTube is a good resources for seeing some of this in action, but you'd do best to educate yourself first, to tell gold from dross. Also, I'm fond of the Osprey books. Not cheap, but wonderfully specific and generally accurate.
That's pretty specific for a time period. Are you already familiar with the era?
1200-1400 covers part of the High Middle Ages and into the Late Middle Ages, so you'll want to keep both in mind for search parameters. You'll be dealing with a wide range of weaponry (two centuries, an entire continent). You might do better to begin with your story and what your characters are using, then go check out information on those specific arms and armor. Or, find a book along the lines of "arms and armor of the high middle ages" and see what strikes your fancy. There are a number of picture books out there. Here's hoping you're near a good library. On this sort of thing, a couple of good books are worth half the Internet.
The 1300s are the period of the Hundred Years War and the Battle of Visby, which are both very significant and well studied cases of warfare and military equipment in Northern Europe. Using these terms should help narrow down the search to results that adress your specific questions.
One of the most amazing things about medieval armor that was discovered in the mass graves at Visby was the really huge amount of fooot injuries among the dead. I don't remember the exact numbers, but one quote I've seen estimates that 70% of all blows were aimed at the legs and another one said that "most corpses had been hit in the legs". This includes feet being completely hacked off and supposedly there's one corpse that looks like it had both legs cut through with a single blow.
While covering the legs is not that difficult, doing it in a way that is practical is a very different story. When marching, the lower leg armor causes the most exaustion. Armor on your upper body is moving at a roughly constant velocity and as Newton tells us, an object in motion stays in motion, unless acted upon by in this case air resistance and friction. You only have to get your upper body moving and then all you have to do is keep it upright. It's a completely different story with the lower leg. With each step, the foot has to get up to speed from zero and then come to a full stop. This constant acceleration and deceleration takes energy, so you really have to consider whether it's worth it to armor the legs. As a rider, you don't have that problem so the answer is an obvious yes, particularly since the legs are even more exposed up on a horse. But for infantry it seems to have been very common to leave the legs unarmored. And apparently the veteran knights attacking the defending peasant army knew that and specifically went for their feet.
As for what armor is used, brigandines seem to be very common for regular soldiers and for knights and men at arms the plate armor is starting to take shape. It's not yet the type that gets displayed as decoration in castles for tourists, but more a mail armor with added plates over various sections. These are pretty decent introductions to the basics of 13th century armor and 14th century armor. Quite the difference in development.
The 14th century is also when cannons are starting to appear on battlefields.
Are there any sources on alldaylife? Not at War or big battles. I have big battles in my Story yes..but there also some smaller Group. Don't know how to explain that. Like traveling from a to b with..say 4 People..not from war to war. More from City to City..and there will also be Fights but more like against Bandits, or a Bar brawl etc.
Would they still be in full Plate Armor? (or like you explained..upper Body in Plate)
Was it usual to carry different Weapons with you, or did you 'specialize'?