How can I verify my ATtiny25 programming? Seeing nothing on output pins
DDRx sets the direction. PORTx determines the output level and presence of the input pull-up resistor.

int main(void)
{
    DDRB |= _BV(PB4);
    while (1) 
    {
        PORTB |= _BV(PB3);
        _delay_ms(200);
        PORTB &amp;= ~_BV(PB3);
        _delay_ms(200);
    }
}