The second definition is about helping others through giving food, money etc.
All these actions are subject to the proper use on the part of receiver. If money is used to buy wine etc donor will suffer. Then what if your money is used for killing others?? The result is hell for many many millions of years. Thus helping others is a problem. Even if you know that there won't be any misuse, how far would you support others? If you offer food to someone in the afternoon, he will be hungry again in the evening. To help others in a real sense means taking others in spiritual direction which would bring them relief according to the spiritual laws and in due process it would fetch eternal bliss.

Coming to the third definition deed is to remember God misdeed is not to remember him.
This what is expected of any human being. Remembrance purifies the heart. Mind keeps on doing of its work of thinking. No one can stop it. Hence that moment when you are not thinking of God you are thinking of its opposite - this finite world. Hence this is an extremely useful definition. First it does not expect you to have knowledge of all spiritual laws. Second this one law takes care of everything. Then it is easy to understand and it is same in all situations. Further through remembrance of God you advance in the direction of achieving your long term goal - eternal bliss.

The fourth definition is that any work done for God is a deed and any work not done for God is a misdeed.
In this type of work you involve God in your day to day activities. For example while getting up you think that 'I am getting up because God doesn't like too much of sleep. I want to see him happy hence I should get up now.' Meaning instead of doing everything for your own happiness you do everything for God's happiness. It is then but natural that you think about God and his liking. Supposing that you like some dish most. You can think that God would also relish this food and hence you will offer that dish to him first and you will eat afterwords treating that dish as his his left over. Similarly when you feel hungry, thirsty etc you offer everything to God first. Thus will treat God like a common person who is in need of everything that you need, of course keeping his divine character intact. In this case your love for God keep on increasing because you are trying to please God through all your activities.

Whether you like you or not, whether you believe or not, your all actions will have outcomes according spiritual laws. It is better to know them to avoid subsequent sufferings.