These are the newer plastic lines.
What does that mean?
Are you talking about PEX?
If so, somewhere there is likely a water supply manifold
that distributes the water to different areas of the structure. Each line has its own shut off. This assumes the system is installed correctly.
If you are talking about simple PVC water supplies then you will have to turn off the supply at the meter (if there is no other main shut off). Cap the the lines, then turn the water back on until you are ready to install the new valves.
As far as the drains go - the toilet drain will have to be plugged, stuff a rag in it or buy an inflatable bulb stop. The shower drain should have a trap in place that will seal off gasses for a short time until the water in the trap begins to evaporate and the line opens.