The pins are shown in this diagram:
The first and second pins are shown here (the first diagram is from the bottom up, the second from the top down):
Your confusion may stem from the fact, that a lot of rotary encoders around foster quadrature outputs. This encoder puts out a gray code instead. I.e. the four output pins are the bits of a series of numbers where only one bit is changing between two positions. This means, this encoder provides an absolute position but can be used as a relative encoder as well. You can use three XOR-gates to generate an single interrupt for rotation detection.
Connect the VCC of the arudino to the pin 5 of the roatary encoder, and connect pins 1-4 to the arudino (or just one of the pins if you only need to detect one rotation). You could use interrupts to toggle code whenever it detects a rising or falling edge