For example, trying to place the third Rune of a Runeword into the third socket while sockets 1 and 2 are empty will result in the Rune filling socket 1, contrary to intentions. Low Quality, Superior, and Ethereal can be used, but you can not use magical, Rare, Set, Crafted, or Unique items, even if they have the correct number of sockets. If defense isn't important, look for an item that looks good, has low requirements, and for armor and shields, is not going to slow your running speed. Same with Armor if you are after Defense and shields for blocking percentage. For weapons you'll want to find the best type of weapon possible, since that's what the bonus damage is based on. Look at the rune list for information on how to get the right runes.
Runewords are a way in Diablo II to use a combination of runes in an item to give it exceptional attributes, beyond what the runes themselves accomplish.There are 78 runewords in total.