PBC in ABAQUS

Hello everybody, i am new in abaqus, is anyone who knows how to apply periodic boundary conditions, for example for unit cell. The piece of code would be very much appreciated

for example ´

if i have on the left hand side node set NSET1, on the right hand site NSET2 than i should use equation like this for periodic boundary conditions in x-direction?

*EQUATION

NSET1, 1,1, NSET2, 1, 1????

Please help 

Best regards

ABAgirl