In order to play casino games online you need to have at least a computer system and an Internet connection. The exact specifications when it comes to the parameters depend on the casino software you want to use.
You almost certainly need Windows as the operating system on your computer. It’s often impossible to play if you use Linux or Mac, though sometimes you can still enjoy the instant browser versions of games instead of the downloadable ones. Windows 95 is usually the minimum requirement, but obviously the newer your system is the better.
The processor speed in your computer is important in order to load and display graphics and other elements efficiently. The minimum ranges from 200 MHz to 800 MHz. Microgaming has higher requirements because of their advanced animations, sound effects and visuals.
Hard Drive memory is where all the downloaded software is stored, so the more games there are, the bigger it needs to be.
RAM is a different kind of memory, only used to playing individual games. The requirements go up if you choose heavy games full of high quality elements, such as Microgaming ones.
Dial-up Internet connection is not recommended at all. 56 Kbps is the minimum speed. Anything lower has similar side effects to low processor speed. Disconnecting is also a problem.
You need to make sure that your computer, or the one you plan to buy, meets the minimum requirements of your casino of choice. The quality of online games is constantly going up, and so are the system requirements.
Specifications can be found on every casino website, for example in FAQ under Technical Questions, on the Getting Started page or in the Download section.