Segwit(Segregated Witness) is an improvement over the Bitcoin Legacy in a way to reduce the size to store transactions in a block. The benefit of Segwit is that more transactions can be accommodated and hence the transaction fees can be lowered significantly.
Bitcoin Legacy addresses generally start with "1".
Segwit addresses generally start with "3" or "bc1". Here you must note that "3" is for P2SH nested segwit and "bc1" is for native segwit.
The transaction fees for spending a segwit output is much lower than that of a legacy output.