A free spin is essentially an offer that a casino gives to its players to spin the reels free of charge and have the opportunity to win real cash. The free spins may be given to both new and current customers, and it's one way to reward and encourage them to continue betting.
Malaysia is a small South-East Asian country, and a regional economic power horse that attracts new investments to an emerging region. Malaysia is predominantly Muslim country, and all forms of gambling are formally illegal. The ban is loosely enforced. In practice international online and mobile casinos do accept clients from Malaysia.