If the employee is outside the U.S. and has no H-1 visa stamp or has an expired H-1 visa stamp in the passport, he/she needs to apply for a visa at a U.S. Consulate abroad. See a list of U.S. consulates.
An overview of procedures is available here.
List of documentation required for H-1 visa stamp:
Note to Canadians: Canadian citizens are not required to apply for a visa stamp. However, they should prepare the above documents for presentation to a Customs and Border Protection agent at the port of entry.