Help on my first line tracking robot please :(

Hello.
https://www.societyofrobots.com
This is a great website for you, especially since you are getting started with robotics. It has many other great articles which you should read, including:
"SCHEMATICS - INFRARED EMITTER DETECTOR" which gives you much information on how to do what you are looking to do. Link:

https://www.societyofrobots.com/schematics_infraredemitdet.shtml
-Omar

I have already visited that site., thanks., but does the circuit work for almost any type or model of IR pair?! thanks

That schematic is a basic one, it should work.
The resistor value is a 'generic' value; it worked for him under certain conditions, but can't be guaranteed to work for you. Thus you will need to do some testing yourself. With that resistor, build up the circuit (temporarily) and then try to shine the light on a white paper, than a dark paper. (Have your multimeter connected) and see what the values are. If the difference between the values is not very high, you will need a different resistor in place.

-Omar
EDIT: Just noticed, shouldn't this be in the Robotics forum?