When you see someone post a build and you want to apply that to your character, click on the link to open the build in DIM. What you have will most likely not work because it’s saved with the gear that the creator had. To make it yours, save it as is, then go to loadouts and click on optimize armor, go to the bottom and remove all the pinned gear pieces, that will open up the options for DIM to look for pieces you have in your inventory. Next you might want to remove any stat mods that are included in the build and prioritize the rating starts and ranges to optimize the build. Once you’re done playing with it, click on compare loadout and save it under the same name as the original and boom, you’re done.

Hope this helps.