Writing a call option consists of creating an option to sell shares to someone who initially buys the call option and subsequently exercises it before expiry. Those who write call options typically have ownership of the underlying security or commodity. Those that don't are termed to have written a 'naked call option'. Writing a put option involves creating an option to buy shares from someone who initially buys the put option and subsequently exercises it before expiry. The risk of options varies with the type of option.
Call options are more riskier because there payoff is unlimited.
Call options are concerned with the upward movement of a stocks price. Considering that stocks can increase without bound, call options are the riskier of the two. Put options are limited to the given exercise price. Puts are concerned with the stocks downward movement. Since stocks can only decline up to zero, put options are less risky than call options.