The option you buy must have many previous buyers before you jump in. Otherwise you might not find a seller. We like options to have an OI of 300 or more. We also like to see that other people are actually trading the option the day we buy it. With a put, you are betting that the underlying stock will go down.
Options are risky enough.
Shorting a call or a put will get you money up front, but the potential loss from being wrong is huge. We never short options. The price at which a stock can be bought if the option is exercised. Of course, we never do this. We just trade the options themselves.