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:
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.
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.