T1 = a wan circuit of 1.5 mbps

ATM IMA = Aggregation of T1s to provide ATM services, at speed in multiples of 1.5 mbs

FR multilink (aka FRF.16) = Aggregation of T1s to provide FR service, at speeds in multiples of 1.5 mbs

MPLS = a network technology that as primary service routes IP packets for a private network, allowing any arbitrary range of addresses to be used, and is largely indipendant from L2 technoly used.

How they work = read on cisco website and many others.