The release of MS-DOS goes back to 1981. In a sense, Batch files could indeed be treated as something that was old since so many decades.
Computing has evolved a lot since 1981, and the job computers do as well.
Batch files help batch repetitive things that you wish to do using a command line. Simple batch files are just sequence of commands. Little more feature reach batch files would have conditional commands and loops.
This book will help you write (and read or extend) some basic batch files.