The interaction of a jet with the stellar envelope in a Collapsar has a crucial effect on the jet late-time evolution and on the properties of the GRB which eventually forms. We preform an analytical analysis of the propagation and collimation of a jet inside a star from the moment of creation until it breaks out to the surface, and afterward when it expands freely. We estimate the jet parameters, Lorentz factor and collimation angle, at break out as well as at late times. The analysis allows us to estimate the minimal energy required to produce a GRB, and to relate the GRB observables to the properties of the progenitor. We also discuss the case when the jet fails to reach the stellar surface, the so called failed GRB, and examine the observational consequences of such an event.