[Oldbluoval]

You get the fender back in proper shape off the car. This might include removing previous welds, patches, bends, bad body work,’damage of most any kind. This usually requires body work skills acquired by experience. Once the fender looks visually correct, loose fit it
To the car. It should mate to holes in the frame. See how it mounts to the RB. RB brackets can be deceivingly bent also. Then see how the fender bracket mates to the fender.
If front fender, both fenders with both brackets and the light bar should be tightened to see that stress isn’t caused by the full assembly.
Basically, your asking for a brief explanation of years of body work experience
There is no Cliff’s Notes version of such.
Go to YouTube and do some searching. There’s a wealth of
Info there