Pattern index matters a lot for certain skins. Like with Case Hardened weapons, blue patterns are worth way more than regular ones. Same gun can be $50 or $500 depending on the pattern. Float values range from 0 to 1, where closer to 0 means better condition. I used to buy random skins without checking these things and overpaid constantly. Found all this info explained clearly at
https://dmarket.com/cs2-wiki/ which shows how different factors affect skin values. Really wish I knew about float and patterns when I started collecting