In VoIP, audio samples are placed into data packets for transmission over the IP network. Typically, a single packet contains anywhere from 10 to 30 milliseconds of audio. TCP and UDP are two of the most commonly used connection protocols used for data traversal across the Internet.
Data travels across the Internet in packets. Think of them like letters: Like letters, the packets have an envelope with a to/from address on them. TCP and UDP are just two types of envelopes. They both carry data and both use IP addresses, but the outside envelope is different. Think USPS versus FedEx. The address on the envelope is the IP address for where the packet came from (source address) and where it's going (destination address). TCP is so prevalent on the Internet that it's typically combined with IP and written as TCP/IP.