How to get started? Buy Basys3 board? NO!!!!
As first step I recommend to use GHDL (homepage: http://home.gna.org/ghdl/) to simulate VHDL execution. Next step is to use also VgaSim (homepage: http://vgasim.sourceforge.net/) to be possible to simulate VGA output.
Of course next step is to adopt Basys™3 Artix-7 FPGA Board example project (source: https://www.digilentinc.com/Data/Products/BASYS3/basys3_basic_demo.zip) to run on simulator.

Any questions and ideas?