Abstract : The thematics treated in this manuscript illustrate two specificities of ultracold metastable Helium gases: the ability to compare experimental measurement with precise theoretical evaluations (simplicity of the atomic structure) and to easily detect products of Penning ionisations. We present the building and the characterisation of a novel magnetic trap with large optical access, allowing to combine the production of a Bose-Einstein condensate with its in situ loading into a 3D optical lattice. The theoretical fundaments of the experiments planned in those optical potentials are then detailed. In a crossed dipole trap, the influence of the magnetic field, now a free parameter, on the Penning collision rates can be measured and compared to a new theoretical evaluation. Concerning Helium in optical lattices, two subjects are developped: the effect of the confinement on the inelastic Penning collisions (1D optical lattice) and the modelisation of the Penning losses via a dissipative Bose-Hubbard model (3D lattice). Finally we present the first direct measurement of the dipolar magnetic transition 23S1 to 23P2, linking the singlet and triplet families in Helium 4. This spectroscopy experiment, realised in collaboration with the group of W. Vassen (LaserLab - Amsterdam), combines cold atoms knowledge with the frequency comb technique, in order to reach an accuracy of 5 kHz.