Everyone loves the tales of knights and the fantasy of the shining armoured man coming to rescue the woman to whisk her away on his white horse. This is fable and myth, knights did have a standard of code that they had to live up to, but they were men just as they are today. Some better with their honour code than most, others rough with years of battle scars.
The main function of knights was fighting. There were trained to protect their Lord's home and go to battle when needed. He fought for his Lord, for glory and the greater good of God. Because the warlike men were opposite of Christian theories, the Church embellished a code for justice, right, piety, the church, etc. This was to save his soul from the endangerment of hell. Every knight had on his person a saint's relic, mainly embedded in his sword.
The most recognized feature of a knight's clothing, besides the armour, was his surcote. It was discovered that wearing this garment over their heavy chain mail kept the Sun's heat off and making it more comfortable. They began decorating it with emblems sewn or painted to the chest so that they could be recognized in battle or tournament. They evolved into the family's coat of arms.
When armour or chain mail was not in use, it depends upon their wealth as the casual wear. One would mainly wear woollen garments, but with a bit on money linen or satins were the flair. The leggings were tight and depending upon the year in the Middle Ages as to the length and style of the tunic worn with it. Earlier years they could be as long as the ground covering all, the length shortened over the years to a waist coat similar to some jackets worn today. Their shoes were thick cloth or leather folded over the foot and tied by laces to hold in place.
The armour was usually fitted over woollen underclothes and attached by leather straps and buckles. The main parts of plate armour include the helm, gauntlets, gorget, breastplate and greaves. They were generally custom-made for each person, so this was a very expensive operation. Your level of armour showed your level of wealth.
Chain mail covered the woollen underclothes as added protection and cushion in blows. Helmets changed over the years and what area they lived. Some were simple cylinders with a flat top, others ordinate in design and decor with feathers and the like.
There were breast and back plates of different names, coverage and designs. Their coat of arms was usually imprinted in the inside for identification. For the rest of the body there were plates guarding the elbow, shoulders, thighs, knees and shins. Just as soldiers today are trained to work with their large loads and uniforms, the knights were quite apt at handling the armour needed in their trade.
To be on the ever ready, most wore their woollen undergarments and chainmail with his surcote over it all for identification. If there was a confrontation during the day they at least had some protection for the fight. The height of fashion would be worn for occasions in which they visited the Lord, parties or dinners.