1.: An FPGA is manufactured to be easily reconfigured by developers, designers or customers. To program an FPGA as a specific configuration, Verilog HDL or VHDL (Hardware Description Language) is used as the standard language for FPGA programming.

2. Gate-Array : An FPGA consists of an array of programmable logic gates/ blocks such as AND, OR, XOR, NOT, memory elements, DSP components, etc., and reconfigurable interconnects which are to connect logic gates together for performing a specific function.

Let's take a very basic example on how to use an FPGA. Let's assume that you are designing a 1-bit full adder and you already obtained the logic diagram of the adder as shown in the figure below.

As mentioned above, there are necessary logic gates on FPGA such as XOR, AND and OR in order to implement the above adder on FPGA. To demonstrate the operation of the adder on FPGA, either Verilog or VHDL can be easily used to connect those gates together as shown in the logic diagram of the adder.