Genes are parts of our DNA sequence which carry information for the production of proteins. They are located in 23 pairs of human chromosomes. Chromosomes appear in pairs: one comes from the mother and the other from the father. Thus, every person has two copies of each gene (with the exception of sex chromosomes in males).
One variant from a given gene is called an allele. The two alleles can be identical or different. We all have the same genes, it is just that some people have different versions (variations in DNA sequence).