If you want a SDR receiver (Rx only) that doesn't require a Ham license, you can buy either DX Patrol or RTL-SDR v4 (or v3). Both should work on GNU/Linux with gqrx (on Windoze, you probably need SDR# aka SDR Sharp). But pls note that there are a ton of counterfeit clones of the RTL-SDR. You should buy it from the Ebay link in the official RTL-SDR site (included in OP).
If you have a Ham license, you can buy a QUANSHENG UV-K6 (or UV-K5) walkie-talkie. Then install the IJV firmware via the programming cable (make sure that the package you buy will include the programming cable!). The homebrew firmware basically unlocks the radio and add some nice goodies. I heard that the stock antenna is very bad, so don't use it for transmitting without testing it with antenna analyzer (ask at a local Ham club). If you want a portable radio transceiver with okay antenna, you should buy Baofeng UV-82 or Wouxun KG-UV6D but note that you can't unlock the radio on these models (you need to have QUANSHENG UV-K6 or UV-K5). If you want, you can build a J-stick antenna relatively easily. You want to reference ARRL Antenna Book, ARRL Handbook and Cebik antenna collection. You can also use 4nec2 software for simulating how your antenna works.
If you don't want to spend any money, you can use WebSDR to listen to radio transmissions. There are free servers in many locations over the world.