You decide whether a substance in homogenous or heterogenous by it's appearance. If it looks like it has just one part, it is homogenous. If it looks like it has 2 of more parts, it is heterogenous. An example of a homogenous substance is mouthwash. It looks like it is one substance, a blue liquid.
No. Homogenous means that the mixture would have the same composition throughout. Beef stew would have more meat in some places and more vegetables in another, etc. Water would be an example of an homogenous mixture.
In a homogenous mixture, the different components are not readily discernible. In a heterogeneous mixture, they can be seen and sometime separate of their own accord. For example, oil and water is heterogeneous, while salt and water are homogenous.