We carried out united-atom Langevin dynamics simulations of polymer's equilibrium state in a good solvent. Our primary goal was a pedagogical exposition of fundamental equilibrium properties of isolated polymers in dilutions with a model that contains many features of real materials. The polymer was chosen to be a three-dimensional chain of N identical beads (monomers) without internal structure. Each monomer interacted with its two neighbors by a harmonic potential, which modeled a chemical bond. Additionally all monomers within a chain were assumed to interact through the Lennard--Jones (LJ) potential. Interaction with solvent and with other polymers was introduced using Langevin forces. Analyzing internal energy per polymer and radius of gyration as function of temperature we observed a rapid globule to coil phase transition. Also we studied elastic properties of single polymer chain for temperatures below the transition and identified three regions with different elastic behavior. Typical chain lengths in our simulations ranged from 100 to 1000 monomers. The elaborated software package can easily be modified to study  {e.g.} the effect of polymer stiffness on thermodynamic behavior.

PACS numbers: 05.45.Xt, 05.45.Jn