These three represent the verb «help» in English. Using each of these words, we are talking about the fact that someone performing certain actions, facilitates another person fulfillment of its task. The most common meaning of the word is a help. In using this verb, you can designate any physical, material, moral, intellectual assistance.
Please, help me! — Please help me!
He helped her off with her coat. — He helped her out of her coat.
He helped me with money. — He helped me with money.
More often than the other two synonym, the word help determine the physical assistance in any productive activity — to help smb. to build a house — to help someone build a house.
Verb aid, as well as help, suggests that assistance is provided when it is really needed. Very often, these two words are interchangeable, for example, when we talk about a difficult financial position of the person or of the obstacles that he must overcome.
He can aid you out of the car. — He can help you out of the car.
If she is in need I am willing to aid her. — If she needs something, I want to help her.
His brother aided him with history. — The brother helped him with the story.
Verb aid is often used in cases when it comes to abstract actions (to aid in the preparation for the funeral — to help with funeral arrangements).
The last of our synonyms assist denotes assistance when we do most of the work themselves, and someone participating in this joint activity on the sidelines, often under our direct management. As the translation of the verb fit the words «to contribute, to participate, to be present.»
She was assisted to her feet by a passer-by. — Passer helped her up.
The army arrived to assist in the search. — To assist in the search for profits armed forces.
He’s assisting the police with their investigation. — It helps the police in their investigation.
All three run synonym direct object that determines the recipient (to help / aid / assist somebody), and two indirect. The first activity of designating the recipient, can be expressed by an infinitive (often without verbs to with help and aid), gerund with the preposition in, noun, prepositional noun phrases: to help / to aid (to) smb. find a new job; to help / to aid / to assist smb. in writing a novel; to help / to aid / to assist smb. in preparation for the examination; to help / to aid / to assist smb. out of a car.