Tcp is connection oriented service which means every time you send a message you get an acknowledgment from the receiver stating the message has been received.
This is a reliable way of communication, but is slow. Think of it as a telephonic call. Only when the other side picks up the call, you can talk.
UDP is connectionless service. Like the one we use in online streaming. There is no acknowledgement in this case so the data might not be perfect at the receiver but the transmission is fast. So a few packet loss doesn’t really matters. It is like an email. You can send but you wont know if it has been read or not. Like you wont know which packets reached and which were dropped.