approximately 5kgs of fissionable material and 30-40 blasting caps placed all over the surface rigged to go off simultaneously.
I'm not going to tell you how to get your hands on uranium ore, but you can convert uranium ore to uranium oxide by acid extraction of the uranium material from the uranium ore. Sulfuric acid is used in this step of the process. The extracted material is crushed into a coarse powder, this is yellow cake uranium.
The yellow cake uranium, aka Uranium Oxide is mixed with hydrogen fluoride and fluorine gas and put into a gas centrifuge that spins fast enough to separate the U-235 isotopes from the heavier U-238 isotopes
Less than 1% of the uranium is the U-235 your friend needs to make a nuclear weapon. You'll need several tons of ore to produce enough material to create a worthwhile bomb.
Once you have 5KGs of U-235, put all the blasting caps around it spaced evenly apart so that the explosion is directed inward towards the core of the material equally. This *should* be enough to start fission and therefore create the nuclear explosion you're.. I mean "your friend" is looking for.
Good luck, have fun.
Remember that breathing in uranium dust can be deadly. Perform all steps with the proper safety material inside a fume hood with adequate ventilation.
Alternatively, your friend can get about 5 million dollars worth of lead panels approximately 6 inches thick, and make about 1000 gallons of heavy water
Make your own nuclear reactor, a small % of U-238 will be captured in the heavy water and convert to PU-239. Follow the same steps above, but with Plutonium, the amount of fissionable material you need to sustain critical mass is much less.
Have fun