The term gene has been defined (by Wilhelm Johannsen) much before we even knew about the structure of DNA (by Watson and Crick). As such, a gene is typically a vaguely defined functional unit in the genome that codes for a gene product (typically a protein). Have a look at the wikipedia entry for more info.
For a given gene, you might have different variants. Such variant is called an allele. Let's consider a given phenotype such as eye color for example. There would be a gene that we could call "EyeColor" and there could have different alleles at this gene that we could call "BlueEyes", "BrownEyes", "GreenEyes", ...
Of course, in reality it is rarely that easy. A given phenotype is often the result of the interaction of alleles at several genes. Also, the environment (type of food, temperature and many other things) affect a lot the phenotype of an individual.
From your comments, it is made clear that you do not understand the interplay of the different factors that affect variance for a phenotype in a population, you have to understand the concept of heritability. You might want to read Why is a heritability coefficient not an index of how “genetic” something is?.
Genes are found in chromosomes
This sounds like a chromosome is a box containing genes which is misleading. In this regard, I like the folded shirt analogy by @terdon below in the comments.
and their job
In science, always avoid the concept of purpose, of goal, of intention. Things just happen.
is to show us
As if genes wanted to please humans. Sounds very wrong.
the traits of someone (height/hair color)
Genetic variance in population does affect phenotypic variance in the population indeed.
Answer to comment
just want a clarification on why genes are found in chromosomes isn't clear?
No, it was not clear and it still is a bit unclear (but I'll give some info below that will hopefully help). The easier for you is probably to have a look at an intro course to molecular genetics such as this one by Khan Academy for example
DNA is found in chromosomes, and large strings of DNA are genes so why?
DNA is a big molecule which contain the genetic information. It looks like that
To be more accurate the genetic information is held in the sequence of base pairs (base pairs shown on the figure). In eukaryotes (animals, plants, fungi and others but not bacteria, archea or viruses) there are several big molecules of DNA and each one is organized into a chromosome. Here is a drawing to help you visualize that
If you screen through a human genome, you will realize that the vast majority of the sequences of base pairs are not within genes. There are many other sequences such as regulatory sequences, repetitive sequences and other things. Note, also that within a gene (but again the term gene is typically poorly defined) not everything will end up coding for a protein. Only about 1.5% of the human genome directly code for a protein.
Giving you a complete answer would require writing way too much. It is much simpler to seek for further information on such introductory questions in a introductory course to molecular genetics (as the khan academy course I recommended earlier).