Documentation is important. Graded academic work will not be accepted without proper documentation. By submitting academic work to be graded, you represent it to be your own work except as documented. Thus, always document all help that you receive. Documentation consists in specifying from whom the help was received, the extent of the joint effort, and the depth of the help.
Documentation is required for all graded homework.
The only exception to this requirement is random, no-notice homework collection. In some cases you will work as a member of a group and the group will submit its work for a single grade. In these cases, help received and material generated within the group does not have to be documented. However, sources outside the group must be documented. This allows us to distinguish between someone who didn't require documentation and someone who forgot to document.