On the second error, you need to compile the program before you run it. First of all, if you are using geany then make sure you ran the rcbasic_geany_config.sh script. You will need to close geany and restart it. After that, whenever you open a *.bas file you can compile it from the Build menu in geany.
Alternatively you can open a terminal in the same folder as the *.bas file and type this"
rcbasic_build name_of_your_file.bas
This will compile your program to a *.cbc file. After that you can run it with this:
rcbasic name_of_your_file
You don't need to include the cbc extension, rcbasic will automatically load a cbc file with that name if no extension is given.
As for your Init Error, that seems to be an issue with SDL2 failing to initialize its graphics subsystem. Make sure you have your graphics drivers updated and try it again and let me know if it is still giving you problems.