You can freeze citrus in many ways, for example if you wanted to freeze lemon, lime, or orange zest then a good way to do this would be to place then zest in an ice cube tray with some fresh juice from the citrus to keep it hydrated and then freeze.
The best way to freeze freshly squeezed juice is to use ice cube trays. And if you are freezing segments or slices, you can place them in a Tupperware box with greaseproof paper between each layer.
You can also freeze whole items much like any fruit or vegetable, just be wary as if you freeze a lemon, lime or orange, when it defrosts it will tend to go a bit squishy, so you may not be able to zest it or save the juice. It is generally better to freeze it in bits than as a whole item.