Discrete Effort: Something that results in a product, service, or result. Using a can opener to open up a can.
Level Of Effort: Activities like coordination, project management activities, budgeting, planning etc. Example would be planning to open up that can with a can opener.
Apportioned Effort: This could be things like inspection, testing, verification. They usually hold a supportive role in relation to a discrete activity. These activities may not be able to be divisible from work work packages. An example would be quality assurance which is done across an entire manufacturing process and thus cannot be divided up.
Hope this helps.