does the negative modifier go after or before the percentage, i've heard a few ppl talk about it but people have told me seperate things

What do you mean?

Okay, so Armor/Magic Penetration works like this; Flat modifier first, % modifier second. Shred goes % first, flat second (or at least, it used to; Riot never said they changed it but someone changed it on the wiki).

So, if they have 100 Armor, and you have 20 flat and 46%, you'll be attacking as if they had 43 Armor (100-20=80, 80*.54=43), not 34.