Basic notions and methods of investigation of discrete equations. a) Discrete calculus (some difference relations based on corresponding continuous relations). b)Difference equations and systems. c)Basic notions used in difference equations. d)Equilibrium points, periodic points, eventually equilibrium points and eventually periodic points. e)Stability of solution, repelling and attracting points and their illustration on examples. f)Algorithms of solutions of systems of discrete equations and equations of higher-order, the case of constant coefficients. g)The method of variation of parameters. h)The method of variation of constants. i)Transformation of some nonlinear equations into linear equations. j)Difference equations modelled with the aid of sampling.