It is called an inline 4 cylinder because the cylinders are all arranged in a straight line. In a V6 the cylinders are arranged in a V with 3 cylinders on each side. There are many 4 cylinders our there that make more horsepower than V6s. Without getting to technical a V6 will usually be the larger engine with more liters because their are more cylinders, a 3.5 liter for example as compared to 2.0. Size is the first differnce.
Inline 4 cylinders typically make most of their horsepower in the upper rpm range. They are high-revving engines that have redlines in 7000rpm range or so. V6 engines make their horsepower at a slightly lower rpm. This all has to do with the size and design of the engine. Where the engines make their horsepower is the second difference.
Of course you have to look at the torque differences. Usually more liters translates to more torque. So V6 engines usually have more torque than inline 4s. Also V6s usually have more low end torque (lower rpms).
Ok lets say you 200HP Pontiac G6 and an Acura TSX
3.5L V6 (201 HP @ 5600 rpm, 220 lb-ft @ 3200 rpm)
2.4L I4 (200-hp @ 6800 rpm, 166 lbs-ft @ 4500 rpm)
The Acura makes its horsepower at 6800 rpm where the G6 is much lower at 5600 rpm. The G6 has more torque than the Acura available at a low 3200 rpm. All of the torque in the Acura is at 4500 rpm. So they both have the same horsepower but many differences. Of course there are other innovations that change these numbers such as variable-valve timing and exhaust, electronic-lift, double over head cams, number of valves, and so on.
Hope that helps.
If 2 cars have same Horse power and one is V 6, the other is V 4.
Does it make any difference? What difference does it make?