There are some terms that may seem confusing in the beginning, but the moment that you know their differences and meanings, you will understand what they mean. Apoptosis is known as cell death. Take note that your cells will die naturally because they are already old and because of different reasons.
When they die, they will usually be replaced by new ones. When you say necrosis, however, this is the time when the cells in your body die prematurely. Sometimes, it is not only your cells that die, but your living tissues can also die too, and this can cause problems, especially if it would happen regularly.
There are different reasons why necrosis may occur. The most common is trauma, getting exposed to toxins, and infections.