There are a couple of ways you can do group tasks: either with Spaces (think of them as folders, and tasks can be assigned to just one Space) or you can use labels (you can assign a task to multiple labels).

I have my Spaces set as Work and Personal, and then I use labels for projects or things like that (so a travel-related task would be in my Personal Space, and labeled Travel).
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Here's how to add them in the task description, and how to filter by them on the board view: