Quantum Mechanics (QM) is primarily a probabilistic theory. The standard Kolmogorov probability theory is not suitable for this goal since it does not offer the possibility of the reversible time evolution. This implies the need to construct a new probability theory which is able to model the reversible time evolution. I have proposed such an Extended probability theory. I offer a possibility to participate in the development of this project which is now partially realized. The main goal of this project is to understand what QM is. The project is now at its halfway. Parts already more or less done are: the local explanation of EPR correlations, the possible locality of QM, the solution of the measurement problem, the impossibility to derive Bell inequalities etc. Parts which ar more or less open are: to explain locally the role of the which way information in QM, to explain locally the delayed choice experiments, to solve the problem of duplicity of the decomposition of the density operator etc.