A job that you do and think "Wow that was unexpectedly easy!" or is it the sort of job where you spend hours googling instruction videos while your DC cry for your attention and you end up having to get someone in to fix the mess you've made of it all in the end anyway?
First decide if it is an oldish tap, which will have rubber washers, or a newish one with a replaceable cartridge, or a ceramic tap where the knob or lever only goes a quarter-turn from off to on, or has a joystick.
In that order, they are cheap, not so cheap, expensive, and buy-a-new-one.
You will have to find the stop-cock before you start, and, after turning it off, see if water stops coming out of that tap. Hot taps, and cold bathroom taps, are often fed from a tank, so you find the stopcock on the tank, and turn that off. Having found it, tie a large, easily seen label to it, for next time.
Have a look on Videojug. You will probably find it so easy that you will want to rewasher every tap in the house. Buy some rolls of PTFE tape and, if you can find it, some white silicone grease. You will need a set of three adjustable wrenches. Tesco own brand will do.