a weapon that you can shoot comfortably, repeatedly, inexpensively while fitting into your lifestyle (for program compliance, ie consistently keeping it in a ready state, being aware of it, practicing with it regularly) is why there is a plethora of weapons available for purchase. for very new shooters, especially women or smaller men, finding a fitting firearm is a task in itself. while explaining all the differences or offering a tutorial is beyond the scope of the question, i do recommend that if you do get a firearm, you choose one with these features:
1. 9x19mm Parabellum/Luger/NATO - this is a very widely used cartridge with over 100 years of history, is inexpensive, and comes in a wide variety of subtypes, and is the most commonly available cartridge among autoloading pistols. prefer to purchase the same 9x19mm ammunition that your local police approve of for duty or off-duty use.
2. a single-stack magazine - a smaller/thinner grip leads to more hand-to-grip contact on the frame of a firearm. this instills greater control of the weapon, more comfortable shooting, and ease of reach for controls. a comfortable gun is a gun you don't feel practicing with is a chore.
3. internal-only or easy-to-understand safety. an internal only safety is a firearm where safeties are completely internal and not user-activated. they often require a handgun be actively held and the trigger pulled than relying on some lever or additional action on the part of the shooter. that is a stress point you don't need to deal with in a defensive shooting. an easy to understand safety can be a simple push button safe/fire (Walther), a lever (Beretta/Stoeger Cougar), or frame mounted lever (CZ 75 Compact). some handguns have a de-cocker only, which merely lowers the hammer to a safe position (SIG P239).
4. a steel frame - heavy guns are controllable guns. it will tame recoil for newer shooters, instill confidence in a physically heavy item (which is a psychological benefit), and if stainless, is usually more forgiving of abuse (dropping it, lack of cleaning). (Smith and Wesson 3913).
for most women, i usually end up recommending a S&W 3913, a Glock 19 (more recently the Glock 43), or a P239. if you have a medium palm but long fingers, consider a Stoegar Cougar.
i tend to not recommend the Kahr or Bersa, because while they are decent pistols, the Kahr can be hit or miss and the Bersa is a PP patterned handgun that tends to "jab" at the web of the hand, making shooting it (practicing) annoying.
a major commitment is program compliance. as in, sticking to the program of obtaining, maintaining, and using a firearm regularly. if you can't commit to that or find that lugging what is effectively a 2lb brick that has a possible murder/wrongful death attached to it isn't something that you can commit to, then don't carry a handgun. i might even recommend you don't buy one if you are unwilling to entertain the thought of possibly being imprisoned for using it. it is a last resort to use in order to save your life from death or great bodily harm.
it is not a magic death laser. it will require maintenance. it will take money and time to get proficient with it. you will have people hate you for it. you will find it annoying to worry about when you don't have it with you. if you do have it with you, it is a liability if you are not ready to use it on short notice. it is worthless in a purse. it is worthless sitting in your closet gathering dust. it can be used against you if you're not commanding enough to exert an affirmative defense from an attack. it isn't a talisman that you can expect to scare people with by its mere presentation.
it is worthless if you are at any point unwilling to kill someone.
