During the game, you will find lots of weapons. They may be dropped by the enemies that you kill, or can be found in chests and on corpses. Each weapon has its basic statistics and you can determine immediately whether the weapon that you found has a higher damage multiplier than what you are currently using or not. For that, use the arrow that appears while approaching the weapon on the ground. What you can also determine at first sight is the item's rarity. This has been described by means of various colors. White represents a standard, common weapon; yellow represents an uncommon one; blue represents a rare one and purple represents a one of a kind weapon. The highest the rarity of the weapon, the higher its capabilities and the stronger its special properties.
It is a good idea to keep various weapons on you at all times. Preferably, these should be all rare or one of a kind ones. The majority of weapons, apart from dealing physical damage, also deals damage from elements. While using them for fighting, you deal additional damage to opponents, e.g. from fire. Often, the effect remains on the opponent and the opponent suffers, temporarily, additional damage from that element. Some weapons also have different effects. For example, the sword called Bizen Osafune allows you to regain health from lethal finishers. There are lots and lots of special attacks and the rarer the weapon, the more of them there are. Often, it is the special attacks that raise statistics of the weapon in specific areas, e.g. block breaking with a strong attack, or frequency of dropping items, or amrita from specific opponents, increased by several percent. Statistics and special properties can be enhanced and increased at the blacksmith's in the starting point. However, this does not come cheap. Especially since you will be replacing your weapons quite often. Statistics themselves are also affected by your weapon familiarity. If you have been using your weapon long enough and you achieve full familiarity of that weapon, statistics go up and you receive more amrita after you bless it in a shrine. You can speed up the process of learning your weapon by using a whetstone.