creating a magic item
 

how do I create a magic item and enter it in so that adjusts the stats?

my DM gave me a cold iron sword +5 Dex + 3 AC +1 to hit

As this is a totally unique weapon you could use the editor to create it. Most likely you will find the idea of putting in adjustments instead easier.

So go to the "Adjust" tab and click on "Other Adjustments" and add three different adjustments.

If you want to use the editor my advice is to read FAQ#2 on how to get started.

adjustments
 

thanks for your response

so if I use the adjustments tab it's a global adjustment and would apply to whatever weapon I was using correct?

It depends on the adjustment you pick. For example the Armor Class adjustment affects the Character but the Weapon Bonus allows a drop down selection to apply the +1 to hit to a single selected weapon.

A) Thats a sweet blade.
B) The Dex bonus will give you some issues, it depends on what type of bonus the DM deems that to be. Since same bonus types don't stack, you'll need to check to see if they character has any other Dex bonus, such as from gloves or a belt, and then take the greater of one. I would recomend making a unique magic weapon in the editor for it, or through the character magic weapon editor on the character sheet.
C) Same problem with the AC, depends on what type it is.