Why do we need 2 sets of a single chromosome?
Gametes are haploid sex cells (i.e. they are cells with only a single set of chromosomes).
When two gametes fuse (i.e. fertilization), then the maternal set of chromosomes comes together with the paternal set of chromosomes.
From there some dominant genes of the father are expressed and some dominant genes of the mother are expressed. This way your physical characteristics are similar but different to your parents, which is important, given that from a natural selection point of view, every new generation should evolve and "improve" with respect to the prior generation.
There is another really important reason for why you have two sets of chromosomes. Your name is Peter, so I will assume that you are male.
Your sex (gender) is determined by the types of your 23rd chromosomes.
If you have an XX arrangement, then you are a female. If you have an XY arrangement, then you are a male. You may ask yourself now: So why do we not just have a single X chromosome for females and a single Y chromosome for males?
The answer is: Because the Y chromosome is much smaller, it does not carry certain genes that the X chromosome has. So males need the X chromosome to survive, whilst the Y chromosome "modifies"/changes their sex.
There are plenty of other reasons for having two sets of chromosomes, but I think this should do the trick for you