Glad you asked
During the campaign, he outlined a series of steps he could take immediately, largely using executive power.
He repeatedly promised to “eliminate every unconstitutional executive order” -- referring specifically to Deferred Action for Childhood Arrivals (DACA) and Deferred Action for Parents of Americans (DAPA), which granted legal status to illegal immigrants brought to the U.S. as children, or who have children who are citizens or legal residents.
Additionally, he has pledged to suspend immigration from terror-prone regions where vetting cannot be properly done. And he's vowed to instruct the State Department to “immediately suspend the Syrian refugee resettlement program” and develop a plan for a safe zone in the region.