Selecting the proper mosfet
For a beginner all there parameters are overwhelming, I'm sure.

The best advice I can give is: do what others do.

So look on the internet (this site even) for something similar, to switch on/off some load working at a higher voltage using a micro controller.

Most of the parameters you mention are not relevant for switching something on/off, assuming you switch slowly, less than a few times per second.

You're looking for a MOSFET and that might not be the best choice as your microcontroller runs on 3.3 V and most MOSFETs really need a bit more like 5 V at least. Even the 2N7000 NMOS I often use has a maximum Vt of 3 V which would leave little margin to 3.3 V. If you find an NMOS with a max Vt of 2 V that'd do fine.

Since you're only switching 30 mA you can use a generic bipolar transistor as well. The voltage of the load is 24 V so Vce,max should be more than that. No worries, most transistors can handle 40 V or more.

A common BC547 can easily handle the job so I suggest to use the following circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

I'm assuming you want to switch a relay and then the flyback diode (D1) is important as it prevents Q1 from damage.

If the load is not inductive (LEDs, resistor, lightbulb) you can skip D1.

The BC547 is a model that's popular in Europe, in the US you could use a 2n2222, it will do as well.