There are a number of circumstances that affect the to-do period a to-do item will be placed in.
Tasks are automatically assigned to the to-do period of the work start date, unless you manually override it on the task. For example, if you create a new piece of work that is due to start on Tuesday next week, all tasks will appear in Next week unless you manually update them to be in another to-do period such as Today.
Notes are assigned to the to-do period that is set when you assign the note.
Emails are assigned to the to-do period that is set when you assign the email.
How do to-do items move?
Items can move either automatically or manually:
Automatic movement
Items in Later move to Next week on Sundays
Items in Next week move to This week on Sundays
Items in This week move to Today when the to-do date is today's date.
Manual movement
Items can be moved manually between periods by updating the to-do date. The to-do date can be updated by either:
Opening the to-do item and setting a new to-do date.
Dragging a to-do item to another period in the header. If you were to move a to-do from today to next week, you'll be asked to select a date next week to move it to.
Sorting your to-do list and bulk updating the grouped set of to-dos. Once your to-do list is sorted with each group you will see a triple dot options menu on the right-hand side. Here you can set a new to-do date for all of the to-dos in the group.
Once moved, the items pick up the new to-do date and then automatically move as per the automation rules above.