Well, that kinds of depends on what your local water is like.
That means we'll need some more information, namely pH, gH and kH, you can get all of that information from your local water authority online.
If you're unsure what to look for on their website, look under something like Water Quaility for your area and then either copy the link or a screenshot and post that on here.
That would be of great help in determing what fish and/or shrimps would do best in your local water parameters.
As for plants, again, a little more information required, are you planning on doing a low tech set up or a high tech set up. Meaning are you going to set up the tank with co2, intense light system and dosing fertilizers, or just staying with the standard lights that came with your tank.
The dimensions of your tank may help as well as what kind of filtration you plan to have.
Though generally speaking from experience, a 5 gal / 20 litre tank is very limited in what you can stock simply due to the water volume. A single Betta Splenden or shrimps only set up tends to work best.
My own 5 gal tank is a very low tech set up with a simple sponge filter, 6w led tube light and a heater, thats it, decor is two nice pieces of bogwood with low tech plants such as anubias barteri/nana, java ferns windelov and balensae cryptocorynes. And its set up just for shrimps and snails only. amano shrimps, Red Cherry Shrimps with Ramshorn and MTS snails, I have fairly hard water so that also limits to what kind of shrimps I can have but nonetheless I find this a very pleasing tank to have as I do find shrimps and snails very soothing and interesting to watch as well as the tank due to its extreme simplicity and easiness of maintenance.
