For the concrete material you would have to define both elastic properties (poisson's ratio and modulus of elasticity) as well as inelastic properties, which includes both the stress strain relationship (go to Materials, structural, inelastic, rate independent, isotropic hardening, mises plasticity, multi-linear) and the cracking/crushing stress ( Materials/structural/inelastic/rate dependent/concrete). Use element solid65 for meshing. There are several different ways to model the reinforcement. You can draw the rebar as lines (use LINK180 elements for steel) within the concrete, making sure that the concrete volume contains these lines. This assumes a perfect bond between concrete and steel, which is the easiest to do. For the steel material, define both the elastic properties and the stress strain relationship. If you don't want to assume a perfect bond things get a little more complicated as you would have to define a bond material and use element Combin39 for it.   

in addition to the above you can also model concrete using Micro-plane model with newer CPT elements. Micro-plane supports the current technology elements SOLID18x.