So, manufacturing is the activity of assembling, constructing, creating, in a coordinated manner and in a sequenced form something for use either by yourself or for others. If you assemble your own computer by buying or using recycled parts, you are manufacturing a computer. If you are making lemon Juice to sell in a stand, you are manufacturing an article for sale and consumption following a recipe or set of instructions.
So, these examples are simple in order for you to understand, but in manufacturing, a series of steps have to be followed in order to produce a product, an idea, or a thing to sell or consume. You have to research what you want to do (Research and Development, Engineering), you have to create instructions to follow and the steps necessary to finish and test to see if its correct ( Manufacturing Department, Documentation, Quality Control, and Quality Assurance), you have to purchase or gather the raw materials for your idea to make and the final product after finishing(Purchasing, Materials Planning, Warehouse) and you have to find a way to sell what you are making (Marketing, Sales), of course, you need people to help you if the item is big or complicated (Human Resources). and you will need an area to build and electricity or tools to use ( Utilities, Facilities, Maintenance Department). This in a nutshell describes what you do when you manufacture in a bigger scale. Let me know if I can be of service or provide more answers.
If you like making things, then best to start with shop class in high school to get exposed to this, then find a manufacturing company that would give you a tour. This will help you determine if this is what you want to do and what area you would like to get into.
Manufacturing is done first by creating a supply chain of things to assemble. Then building an assembly or factory where parts and supplies are put together. Finally you need distribution to send your finished product. The smallest manufacturers can use 3D printers or hand assembly to start manufacturing quickly and easily change products. The largest manufacturers have machines that cost millions of dollars to change. A great book on manufacturing is called "The Goal". The foundational process described is used throughout factories across the world.
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