Yes, the Precambrian is the largest geological time because it contains 3 eons: Hadean (4,600 - 4,000 MYA), Archean (4,000 - 2,500 MYA) and the Proterozoic (2,500 - 541 MYA). The 3 eons contain eras and many geological periods.
MYA is short for million years ago.