c --- creating
v - verbose name
f --file

here onjava.war file is created in directory where ur java is running ie jvm eg:

d:>jar -cvf first.war second

here u are creatin g war file of name first which will contain all files prsent in second(file name)
if it is present inD drive

actually they are nothing but like our zip files
which will occupy less pace on harddisk
that s it