If you want to do quantum chemical calculations then you have to install the proper software.
It is possible to set up a working system at a low price. Many commercially available personal computers are fast enough to do the job. Those computers that are designed to give top performance for computer games will be perfect for the calculations too. But you may not need the expensive graphic card.
To do quantum chemical calculations you will need software that performs the calculations. A list of available packages is on wiki .
We use GAMESS. GAMESS is a well know software system and the number of possible calculations is really huge. Check out the website to find out how you can get it. There you find all information you need to compile, install and run the software.
If you don't have much experience with installing GAMESS then read this extra information .
You probably need some software to view molecules in 3 dimensions. There are several molecular modelling software systems available, some of them expensive. A popular software is Avogadro. We use Avogadro a free and open source software. We also use MacMolPlt a freeware software.