Here's an octal counter that can display the numbers 0 -7 in three LEDs, using a counter IC. Figure 1 shows the relationship between the decimal numbers 0-7 and the counter outputs displayed by different ON-OFF combinations of LED 1 - LED 3.
The schematic shows you see that the astable multivibrator using a NAND gate generates clock pulses. U2 counts the pulses from the multivibrator, and its output is sent to Q0 - Q2.
Wire the project, turn power ON and see what happens to the LEDs. You'll see them start blinking ON and OFF. Watch the LEDs while looking at Figure 1, and you'll notice that the counter is counting from 0 to 1,2,3... and soon.