Algorithms currently implemented in QMCPACK are Variational Monte Carlo (VMC), Diffusion Monte Carlo (DMC), and Reptation Monte Carlo (RMC). 
This  is intended to introduce key components of QMC methods. For comprehensive reviews of recent development in QMC,  consult review articles and other resources.

Trial wavefunction
Fermion trial wavefunction
For the Fermions, one of a component is antisymmetric under particle exchanges and is given as
Single-particle orbitals (aka one-body orbitals)
Plane waves Molecular orbitals: Gaussian, Slater, and numerical one-dimensional grid Bspline on a 3D grid Mixed orbitals
Variational Monte Carlo
Parameters {α} are optimized. See the discussion on the optimization.
Diffusion Monte Carlo
Projection of a trial wavefunction Population control Weight of a walker Trial energy Periodically updated based on the ground state energy estimate <Eg> and the current population P(t) for the target population P0