MVVM - Can I send an argument with my command?

I am doing a hobby project to learn Mvvm. Currently, I've got a main window with 12 buttons. One for each month and am going to add a few more for year summary. I have a corresponding list of "financialmonth" view model instances named for each month. I need to tell the main view model which month I am looking for, so it can find it in the collection of "financialmonth" view models and set the current view model for the content. Following samples, I haven't seen a way to send an argument with a command and I think I need to.