Express Entry is a system used by Immigration, Refugees and Citizenship Canada (IRCC), which manages and processes applications received through Canada's federal economic immigration programs.
Express Entry is a completely electronic process involving the federal government, provincial governments, and Canadian employers.
Candidates accepted in the Express Entry pool are scored, awarded points and ranked against each other. Immigration Refugee and Citizenship Canada then selects candidates from the pool and issues Invitation to Apply (ITA) to candidates with high points and other factors (such as occupation in demand). So they can submit an application for Canadian Permanent Residency.