What are the Three Trainings and how are they practical? What are the Three Trainings and how are they practical?
Specifically how does one practice them?
The threefold training (Pali: sikkha) consists of: morality (sila); concentration (samadhi); and wisdom (panna).

Sikkha is meant to conquer and eradicate the defilements (kilesas).

Visuddhimagga XXII,49


  'The defilements are the ten states, namely: greed; hate; delusion;
  conceit; false view; uncertainty; stiffness of mind; agitation;
  conciencelessness, shamelessness. They are so called because they are
  themselves defiled and because they defile their associated states.'


Each of those defilements has 3 stages (bhumi) which are identical to the 3 stages of consciousness (latent - manifested - action).


the latent stage = anusaya-bhumi
the manifest stage = pariyutthana-bhumi
the action stage = vitikkama-bhumi


Through the threefold training, it is possible to conquer and eradicate these defilements in the 3 subsequent stages: sila-sikkha; samadhi-sikkha; and panna-sikkha.

The training itself is a strict personal affair: Purity and impurity depend on oneself. No one can purify another (Dhammapada).