Life: That which undergo metabolism, grows and reproduce.
Cell: The basic functional unit of life.
Organism: A contiguous living system.
DNA (deoxyribonucleic acid) is the information storage device of living cells. Amazingly DNA is actually a digitally encoded information storage system.
The living cell is the basic functional unit of life and yet they are still highly complex organized systems of information, structure, molecular machines and much more. Each cell has a level of complexity similar to a city but possesses more organization making even the simplest living cell more complex and organized than any man made machine. Single-cell life includes organisms that are made of only one cell. Examples include bacteria, single cell animals and single celled plants such as blue green algae. Multi-cellular life includes organisms consisting of multiple cells usually billions such as plants animals and people.
In really there are essentially only two possible origins for life: A naturalistic origin called abiogenesis or a supernaturally intelligently designed origin. Other suggestions don’t actually solve the problem but merely move it some place else in the Universe.
Abiogenesis has the problem of overcoming the overwhelming gap in organized complexity between a living cell and the chemical constituents that make up a cell. Furthermore no natural process actually demonstrated to exist can accomplish the task but known natural processes indicate that it can not happen. Going from non living chemicals to a living cell requires reducing entropy by an immense amount and statistical thermodynamics shows that natural processes tend to go towards increased entropy; which is the opposite direction of that needed for abiogenesis. Now adding energy can decrease entropy it only does so if applied in a sufficiently organized manner and no known natural process can apply energy in a sufficiently organized manner to achieve abiogenesis suggesting that abiogenesis is impossible.
A supernaturally intelligently designed origin of life does not have these problems because it is known that intelligents can create complex organized systems because humans do so. It is also known that intelligents can encode a functioning genome because human scientists have done so. Intelligents does have a sufficient degree of organized complexity to create a living cell. Furthermore the intelligents that started life in the universe would have to be from out side it and thus would be supernatural.
It is often claimed by evolutionists that evolution is just change over time in the inherited traits found in a population. If this were really all that was meant by evolution there would be no issue since creationists agree that there is change over time in the inherited traits of a population. The real dispute is with the idea that observed variations can start with one cell and produce all life found on earth including man. Going from microbe to man requires adding a lot of information by nothing but than mutations and natural selection. The Evolutionist argument is that given enough time mutations and natural selection can produce any thing, however such large degrees of change has never actually been observed. They are however a necessary assumption for a totally naturalistic origin of current living systems.