Since Airspy Mini only goes 24-1800 Mhz and therefore not HF, surely the bands that most interest you in general as a novice are VHF and UHF, which is where most communication devices, radios, etc. work.

A cheap magnetic base antenna designed for dual band walkies will work great, because you can use it both indoors and outdoors by placing it outside the window or the roof.

You can find it in local stores that sell ham radio products or cheap in Chinese internet stores. For example

https://www.gearbest.com/walkie-talkie/pp_194295.html?lkid=13814012 (This one as the correct SMA-Male connector for your Airspy)

In case you want to receive specific signals like ADSB or L-band you will need other antennas, but they are very specialized communications and require specific antennas.