In classical genetics, traits —passed-down physical characteristics — are encoded by genes. For each gene, you get a copy from your mother and a copy from your father. (These copies stay separate; they don’t blend together.)
If you have only one copy of a gene’s dominant version, the trait will show up. It will appear the same whether you get it from one parent or both. The recessive version is the one that’s “masked” when a dominant version is present, so for its trait to be expressed, you need two copies, one from your father and one from your mother.