The gathering of Dark Matter is simple, and yet its not. 

The problem with Dark Matter is that it exists partially outside our space/time and thus cannot be easily detected and/or collected. The region of space that it is located is a different dimension that is tied to our own (we have 12 dimensions tied to our universe). For reason of simplicity, we will call this dimension "subspace". 

Dark Matter can be drawn out of subspace using a specially built collector. This collector has been built at the Hanford site, in Washington state. However, they know only a few things about it.

The first rule is: the collector must be left on for at least 6 months to collect a small amount of Dark Matter. This will equal about a gram of the material. Running the machine for a few weeks or months isn't enough time, 6 months minimum to see results.

The second rule is: no Dark Matter Collector can be within 100 miles of another, otherwise it causes "interference" which sabotages the collection process.

The third rule is: Dark Matter must be held in a special energy containment system. Otherwise it will instantly dissipate back into "subspace". No worries of explosions if containment is breached.

Dark Matter is not a power source, that's Dark Energy.

Other important facts about Dark Matter is as follows:

The main reason for collecting Dark Matter is this: a low level electrical field can be applied to Dark Matter, creating an antigravity field. One gram of dark matter is enough to lift an entire aircraft carrier above the Earth.

The Earth itself helps with Dark Matter collection; its gravity field draws more of the material from subspace towards our location. Thus, Dark Matter collection in zero-gravity conditions does poorly.