Most common places in a house is in the basement. Either on the wall closest to the street or in the furnace room. If on the front wall, it can be anywhere on the length of the wall probably 2 to 3 ft. above the floor. There is also one at the meter, but this one may need a special wrench to turn it, also they can be very stiff. If you do not have a basement, I would look next to the furnace and hot water heater.
In the yard between the street and the house, in the basement on the wall closest to the street or if on a slab, between the floor and the inlet of the hot water heater. One of these three places.
With the water main shut of valve of course
I do not live in a condo thus I have no need to shut the main valve
Showers and tubs do not usually have shut off valves on the supply lines. To shut the water off you will have to shut off the main water line. There should be one on the cold water line to the water heater. This may shut both the hot and cold off or just the hot. There will be one in the main line coming into the house on the basement wall closest to the street or at the water meter.
You will get some back pressure from the water heater. It will come out of either the hot or cold. Shut the tank off if there is a shut off there.
Most tubs do not have a shut off in the supply lines to it. You have to shut the main off where it comes into the house.
The water meter is shut off? The main water line is shut off? The valve for that faucet is turned off? The waterline is made of galvanized piping and has corroded shut? Aerator is clogged, remove and clean or replace.
Outside at the main shut off valve. Showers/Bathtubs do not normally have a shutoff valve like sinks and toilets. The main water valve for the house must be turned off.
Tubs usually do not have shut off valve for them. You have to shut off the main supply. Depending on how the house is plumbed, you may be able to shut the cold supply to the water heater and that will shut off both the hot and cold or the main line where it comes into the house.
The valve seat or washer on the main valve are not seating/sealing properly.
No. The Main is source of water for that as well.
Water will run until a valve or pump is shut off upstream from water main break.
If the shut off valve turns but does not shut the water off, the washer in it has split and probably made it to the faucet. It was blocking part of the hole on the hot side and at some point either shifted or made it through the faucet and in in the screen in the end of the spout. Shut the main water off and replace the washer in the shut off valve.