A traditional IPO (Initial Public Offering) works when a private corporation offers shares to the public to raise capital. The process includes a "roadshow" where the company meets investors, and management undergoes intensive discussions with regulators through investment banks which can take 12-18 months.
On the other hand, a Special Purpose Acquisition Company Initial Public Offering (SPAC IPO) works by already having a company go public with the intent to acquire a private company. The process takes 3-6 months on average by raising capital through 'shell companies' which then combine with a private company to take that company public. Startups like WeWork & Grab plan to go public through SPAC IPOs as part of a general trend in 2020 of startups favoring SPAC IPOs over traditional IPOs.