whats the porpuse of the m button on the center console

[luzyfer13]

i have a 97 328is cabrio and it has this feature A and M on the left side of the center console by the shift lever. i was wondering waht is for and how do you operate it? i dont have an owners manual so i dont know. any info?(im new to this site.) thanks in advance and hope i can be a contribution to this wonderful forum E36 for life.