DMRS is a demodulation reference signal, which gives the channel quality of PUCCH and PUSCH data . Enb will decode the DMRS first , If it is succesfull then he will proceeding decoding the PUCCH,PUSCH. If fails he wont decode the PUCCH,PUSCH.
DMRS is a CAZAC sequence, multipke UE will have multiple CAZAC sequence by useiong cyclic shift. this will be configured by ENB to UE.