Hi Jeff,
Although it's possible to import activities through the Activity table, we generally do not recommend it. Activities are heavily linked throughout the entire CRM to many other tables and fields, making this a daunting task. If you do go ahead and try to import activities, I would recommend exporting the Activity table from Method first, and using the same headers that Method uses. This will help to ensure that the fields are mapped correctly. I also recommend doing heavy testing by importing small batches of activities to see how they look in Method before you import a large batch. This way, you can just delete the small batch of imported activities if they are imported incorrectly.
Click here for an article and a series of tutorial videos that will teach you about importing and exporting. Hope this helps!
Jason