The geometry of general structures based on carbon multi-tube contacts is discussed and same characteristics of the electronic transport in metal-semiconductor (6,0)-(5,1) nanotube junction are presented. A theoretic method allowing us to construct the structure of a multitube carbon cluster composed of two or more tubes of different characteristics is developed by introducing heptagonal and pentagonal defects in the hexagonal grafitic net. By definig the "strip" concept, we propose a general classification and notation of these structures and develop a method to determine the indices of the outgoing tubes from the multi-tube structure. We also demonstrate that is always possible to connect two tubes of arbitrary indices with only one heptagon-pentagon pair, and the mehod to obtain the specific geometry of the two-tube union is presented. Electron packet movement in a (6,0)-(5,1) nanotube junction is analysed by numerical integrtion of the nonstationary Schröringer equation in the π-electron tight-binding approxination, using the norm-conserving numeric scheme based on a Padé approach of the evolution operator. The method developed can be applied to a general contact of two arbitrary nanotubes.