Essential is related to Need. Need is related to Help. Mechanism can be used for Help. Control is a type of Mechanism. 
Learn is related to Activity. Activity is related to Organize. Organize is related to Arrange. Stack is a type of Arrange. 
Essential <--RelatedTo--> Need <--RelatedTo--> Help <--UsedFor-- Mechanism <--IsA-- Control 
Learn <--RelatedTo--> Activity <--RelatedTo--> Organize <--RelatedTo--> Arrange <--IsA-- Stack 