I have a "waterfall" faucet in my tub (separate shower). I turned on the water to the tub the other day and it barely runs. Then tonight my daughter was running the tub faucet and I had no hot water pressure to the kitchen. This has never been a problem. I understand from reading that we may have buildup in a line from the hot water heater but it is attached to a water softener.

How do I go about cleaning out a pipe, do I have to take the water softener apart?

Is there any where to get step by step instructions to do this?

Thank you for your time.

How old is your house and what kid of pipes do you have ? How often do you flush out your water heater? How old is the heater? This came on suddenly?
Bypass the softerner and see if there's a difference.
"Then tonight my daughter was running the tub faucet and I had no hot water pressure to the kitchen."
Are you saying that a tub faucet, that has no pressure or volume, is drawing volume away from the kitchen that has pressure when the tub faucet's off?
There's something in your system that's cutting down on volume which directly affects pressure. The fact that opening up the tub valve while making a draw in the kitchen sink cuts the volume off to the sink indicates the problem isn't just in the tub branch but is affecting the entire hot water system. To check this out you must start at the source,(the water heater) and starting at the source go fixture by fixture until you get a drop in volume and pressure. But first, if you have neglected the heater and it's loaded with mineral buildup it must be flushed and cleaned out.
Let me show you how to flush,(not drain) your heater. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) and some white grains,(lime or calcium carbonate). The whole thing shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. You might want to consider cleaning the screens on your areators if you have a high mineral buildup. If thev problem still persists after you have flushed, you will have to drain the heater, remove the boiler drain and go up in the bottom of the tank with a wood or plastic rod, (not metal) and try to break up the mineral and flush it out. Good luck, and thank you for rating my reply. TOM