hi Nimish,
Like u I am also around one and half yr old in this forum & have successfully discussed couple of my own problems.
The reason I feel you are not being able to follw up is there are lot many PLC manufacturers available today. With the same basic principle every manufacturer has got a little varity of hardware & software with the leading manufacturers like Rockwell Automation, Siemens, GE Fanuc, OMRON, Modicon etc.
PLC's are the mostly commonly used automation tools in industries & other miscellenous applications.Primarily, it started as a replacement of hardware relays ( Digital device ) in old times but as we progressed PLC's started doing Analog functions. With more & more manufacturers coming in the field different types of Inputs ( Digital/Analog), Timer, Counter functions started coming. After that came the era of PLC communication with computers & developement of softwares for programming. Now there are many softwares are available. Today PLC's are everywhere from Process industries to our houses where ever automation is requuired.
I hope this introduction will help u little. For more you can always look for PLC tutorial section of the site.