Gene therapy involves altering the DNA of an individual, either before they're born or at some point during their life. Cloning involves making a genetic duplicate of an individual. A clone is just a genetic duplicate, though - not a physical duplicate. For example, if I were to clone myself, my clone would be born like a normal baby, would age and grow at the normal rate, and wouldn't share any of my memories. For all intents and purposes, my clone would be a completely separate individual, forever 31 years younger than me.
Gene therapy is the use of DNA as a pharmaceutical agent to treat disease. Cloning in biotechnology refers to processes used to create copies of DNA fragments (molecular cloning), cells (cell cloning), or organisms.
Take note that gene therapy is applied to treat diseases while cloning can be applied to other biotechnological techniques, depending on the need (example for agriculture) and considering as well the ethical issues.