Grouping tasks by category?

Grouping tasks by category?

I'm new to project management and trying to learn as I go by using Zoho Projects and what makes sense to me.  So far we've been tracking deliverables for a project in an Excel worksheet.  We've been grouping these by broad category, so tasks related to financing go in one bucket, tasks related to marketing go in another bucket.  I had started to recreate these category listings by using Project Milestones, but thinking about it a bit more it doesn't seem this is what the intent of a milestone is.  Some of the tasks under a grouping are dependent on another task, but many are not, and it seems to put anything under a Milestone, you then need to create a task list, and then the task under the task list, which again seems weird.  Am I doing this wrong?