In order to connect your DE10-Nano board to VGA or other RGB output, you need an I/O Board. This PCB board and assembly instructions are available on the GitHub pages of the MiSTer project.
Getting FPGA cores of your favourite retro systems onto the DE10-Nano is very easy. You can run them in matter of minutes.
The Terasic DE10-Nano board is based on Altera Cyclone V SoC chip. It is a hybrid of ARM processor and FPGA that lets you do amazing things, among which is run cores of vintage computers. But as always it is good to start with making a LED on the board blink.
The basic building blocks of FPGA chips are logic elements (LEs). A logic element consists of LUTs (look-up tables), which are basically programmable logic gates. This gate is a multiplexer and can be build out of NAND gates. This small project is a breadboard implementation of this concept.
One of the disadvantages of Altera Quartus II software is the disability to run natively on a Mac system. Luckily there are ways to get around this problem.