How can apply for M visa with multiple entries

If you only go to provide a training, personally speaking, a F type is much suitable. Besides the invitation letter, you still need to provide an personal statement including your basic information, information about your company, information about the company invites you, the place you will go, the company's name, etc; your valid passport, an application with a recent taken photo. Then you still need to contact the embassy to ask whether they still need special documents for your application.