If you speak English, Spanish, or French, the Web site of the United Nations Commission on International Trade Law will work. Repeat the last three steps with a handful of sites and you will soon have a feel for how these programs work. None match human translation. Machine translation programs don't all use the same translation protocol. Some cover more languages than others.
Some programs have bigger dictionaries than others.
Some seem to translate better in one direction than in the reverse. Simple sentence structures translate the best. Some programs are faster than others. Interpretation of the result is almost always required. Machine translations should not be relied upon when accuracy is critical.