It looks like you have another post asking very similar questions. The tutorial in the SourceForge link that Jim posted looks like it goes over dead reckoning and keeping track of x and y coordinates. Is there something more specific that you had questions about?
It sounds like you might be confused about how you can use the pulses (or “ticks”) from your encoder. You should be able to measure the number of ticks you get from moving your robot’s wheel some fixed distance. Then, you can use that information to find out the distance the wheel travels per tick of the encoder. By keeping track of the distance that each wheel has traveled, and knowing the distance between the wheels on your robot (often referred to as “track”), you should have enough information to keep track of your position and angle as detailed in the tutorial mentioned earlier.
Dear Mr. Brandon , many thanks to you .
now almost things came to be clear , but there is one thing need some clarification , which encoder should i got to calculate the position (coordinate x y) and orientation (angle ) of mobile robot ,because as you know there is many types of encoders (incremental , absolute ,…etc.) , I read about each one in the websites but I still confused which one will be the desired for my problem .