LDR is a Light Dependent Resistor, so its value of Resistance change with the light that the LDR receive.
The more light the less resistance.
You must get a network of resistances for example in serial to convert the variation of resistance in a variation of voltage.
+VCC
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Resistance (1K)
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> Analogic input (PIC)
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LDR
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GROUND
As AJISH ALFRED have said before connect it at an Analog Input of the PIC and read the analogic value