This is a no-forma build good right out of the foundry with no primed mods, focusing on farming loot with Desecrate.
It's a beginner build in the way that there's no forma needed and no primed mods. Normal mods can be found cheaply on the market.

Note: The Aura is unpolarized. I thought I remembered [Nekros Prime] had a Vazarin Aura, and I used '[Physique]' long ago when I had a build like this, but I've since put in an Aura Forma and forgotten. Can't be sure, and the wiki reinforced 'no polarity', but I thought for sure all I could put in was a Vazarin. So, if [Steel Charge] doesn't work for some reason, you can safely cut a few points off of [Adaptation].

[Health Conversion] might be the hardest mod to obtain. It's a little pricey on the market. You can also get it from Simaris for 100k standing. Totally worth it for a Despoil Nekros.

For my current forma'd Helminth Nekros Prime build with Primed mods, go here:
https://overframe.gg/build/76827