I'm planning to buy a Samsung Monitor. If I'm planning to play games on it, will it decrease my fps? Also, can I run window games on the monitor?
When playing games, there are two things which determine your "real" fps, i.e., the number of unique or distinct frames you actually see.
Firstly, the monitor has a built in "refresh rate," which is the fastest speed at which the pixels may change color. The refresh rate never changes, no matter what your computer is doing. For most monitors this is 60hz, although high end "gaming" monitors may have refresh rates as high as 144Hz.
The second thing you have to consider, is how many FPS your computer is able to send to the monitor. This is determined by your graphics card (GPU), CPU, RAM, and Hard Drive in that order. Depending on how demanding the game is, the number of FPS your computer will send to the monitor will change. The more demanding the game the less FPS. For example Battlefield 1 and Ashes of the Singularity are very demanding games, Overwatch is semi demanding, and angry birds or candy crush, are not demanding. Macs tend to have very weak GPUs
The number of FPS you actually see is whichever is less, the Refresh Rate, or the FPS output by the computer. For example, if your monitor is 60Hz, but your computer is only outputting 25FPS, you only really get 25FPS.
Finally, the monitor only displays the images your computer sends to it. So in a sense, you can't play any games "on it." However, if you connect a windows computer to the Samsung monitor, or install a Windows partition on your Mac via Bootcamp and connect it to the monitor, then you can view your Windows games on the monitor.