I don't know all the customs and there is a difference between Amish and Mennonite. Mennonites are usually a sect that has broken off of an Amish backround.
For a Man who is married, He usually grows a beard to show that he is married.
Amish wear more plain Clothes- no buttons and dark colors. The women keep their heads covered like most religions and Christianity used to.
They don't have electricity or anything that will tie them to the outside world. They can used batteries and are very good workers. To find out more may I suggest you rent the movie "Witness."