Just want to know if i install OS on the SSD and my games on HDD will they benefit from my SSD speed, and will i gain anything whit this setup for gaming performance or games need to be installed on SSD drive for performance boost?
No, games won't benefit from the SSD unless they on the SSD .... and the improvement frankly is no great shakes. Area loading times might drop say from 15 seconds to 10 seconds. Of course much depends on what hardware ya using.....I'm using a Vertex 3 Max IOPS and Seagate Barracuda XT as reference.
Its very OK to do it the way you said, thats how most setups are done nowadays due to the relative high prices of SSDs. You will not get SSD benefits for loading games if you install them on HDD, but nevetheless, you may get 2 HDDs and RAID 0 them.
The games will not benefit from the ssd by being on a HDD but games dont benefit much by being on an ssd anyways, they just load a little quicker. So just leave them on a standard HDD and use your precious ssd space elsewhere.