How can I learn plc without device perfectly?

You can learn basics of PLC without connecting the field device.All you need is a PLC software with simulator embedded in it and install this software in your Laptop .Use simple ladder language with internal address, for example ( Like One Normally open contact with output coil).Compile the programme, if No error in compilation , use the simulator present in the PLC software and test how it works.
For more on PLC visit ( https://en.wikipedia.org/wiki/Programmable_logic_controller) There are Five PLC Language ( Programmable Language) :1.
LD, Ladder Diagram2.
SFC, Sequential Function Chart3.
ST, Structured Text4.
FBD, Function Block Diagram5.
IL, Instruction List LD & FBD are easy to program me, rest are high level language.
To have a practical knowledge you have to join a training institute or a company which works on PLC projects.

simulators i guess

Yes PLC can be learned without having a PLC Device but for perfection you need to have PLC Device.
You must have the knowledge of input devices and output devices of PLC.
By using PLC Simulator you know programming basics and checking correctness of your logic.
It is good to start with simulators before moving on to physical devices.

use simulation demos...its good for starting rookies..

 

  you can use a simulator like Logix Pro which help you to learn and practice on Allen Bradley perfrctly

You can learn basics of PLC without connecting the field device. you need a virtual machine with PLC software embedded in your Laptop.

There are same basic programs for starter.
http://automation-renew.blogspot.in/2012/10/basic-program-ladder-logic.html Hope its helpful...
Best of luck