connect the resistance in series with the led to protect it from higher current
potentiometer has 3 legs ,out legs connected with the resisto tap inside it and the middle is connection all you need to do is to connect the middle with the any of the outer legs
-you have to know the difference between each leg of the transistor it's npn 547 searc for its datasheet to know about the connection
note that when touching the led and transisitor base LED is turned on because base current is positive one .
using 555 IC
It senses the darkness what makes the LED turns on.
just replace LDR and potentiometer in dark sensor