First law of thermodynamics actually is a version of the law of conservation of energy. Thus, the first law of thermodynamics with the second and the third are just modified for thermodynamic systems. All laws can be viewed differently regarding physics and chemistry. First we need to see what the law of conservation of energy is all about and then we can talk about the first law of thermodynamics.
Аccording to the law of conservation of energy all the energy of an isolated system is constant. Energy can be only transformed, not created or destroyed.
The first law of thermodynamics is about the change of the energy of a closed or an open system. Considering the thermodynamic process, this law uses the key concepts of internal energy, system work and heat. But when we talking about heat engines, discussion can go on forever.
Thus, the first law of thermodynamics states that change of the energy of a closed system is equal to the amount of heat supplied to that system, so that amount of heat minus the work done by the system is the change of the energy. The standard unit for these quantities is Joule, but some express them in BTU.
Actually, it is presented like this :ΔU=Q+W, even though the guy in the video presents the ΔU as ΔE. Q is the heat, it is the power or the energy that enters the system, W stands for the work that the system does.
The guy that uploaded the video on YouTube talks extensively about the simple basics of the first law of thermodynamics. He pinpoints some equations and tells us what to focus on, so check it out!