Cells growth refers to the population of a number of cells, the population grows by the cells using mitosis, mitosis happens when the inside of the cell copies the chromosomes and then divides itself into two separate cells. Which is how they multiply.
Now let's say that you cut your finger on a cheese grater, you have probably damages a few cells. but how does this get better? Well most cells don't repair themselves they use lysosomes to kill themselves and the the body makes new cells by copying the chromosomes in the cell and the splits the apart making two similar cells. Which then eventually fixes the cut.
Meiosis is when two organisms reproduce and two cells meet and make a copy of itself, the cell then has four pairs of different pieces of each organism, then the cells begin to split and multiply with a stage that is similar to mitosis, then you have an organism.
The difference between mitosis and meiosis is that mitosis is when a cell can multiply without sexual reproduction, and meiosis is when you take two cells which will sexually reproduce and make a copy of the two.