This example describes an 8 bit loadable counter with count enable. The always construct, highlighted in red text, describes how the counter should behave.
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behav_counter.v
module behav_counter( d, clk, clear, load, up_down, qd); // Port Declaration input [7:0] d; input clk; input clear; input load; input up_down; output [7:0] qd; reg [7:0] cnt; always @ (posedge clk) begin if (!clear) cnt <= 8'h00; else if (load) cnt <= d; else if (up_down) cnt <= cnt + 1; else cnt <= cnt - 1; end assign qd = cnt; endmodule