If your phone has a USB charge port- as most do- the voltage will be standard, at 5 volts. By default all USB chargers will provide this amount of voltage. If it's got the capability, when you connect it the phone may be able to use higher voltages, like 9 or 20 volts.

Your phone may want more power than a basic charger can deliver, in which case it'll charge slowly- and in some cases, such as a cheap or old charger, may overload the charger causing it to heat up or fail- usually by burning a component.

A higher-power charger may allow your phone to charge with higher current levels (more power), and charge more quickly. This would only apply to USB-C type chargers, the ones that are reversible. Older chargers are more limited in power delivery.

If your phone doesn't use a USB port for connecting a charge cable, you must use a charger with the correct voltage and current for it. I'm not familiar with any modern phone that does this, though.

It depends on the test, but the basic principle is that you have a piece of paper that absorbs liquid and "wicks" it through the fibers. At one end that paper is exposed to a stream of urine that is absorbed into the fibers.

At the other end of the paper is a diagnostic strip that will change color or darken if certain chemicals are present and will not change if they are not- that's looking for the presence of specific substances that are only present when someone is pregnant. There's usually a second strip that's a "control" and will change color regardless of the presence of any chemicals.

So when you use the test, the liquid is absorbed up the paper, wets the two strips, one will turn color letting you know that the test is working and that enough liquid got into the tester that the result is valid, and if the other one changes it's a positive result.

All that said, some testers do have digital readouts. I'm not familiar with how those work, but they cost a bit more, from my understanding.