Female physique examples
Want to know how to build muscle as a woman? The same way a man does.
Here are two women with low enough body fat that you can clearly see their muscles:
The first woman is sometimes considered thin (look at the frailness of her arms) and the second woman is often considered fit.
Feel free to decide for yourself what is normal and healthy. I'm not intending to pass judgment just for the sake of it; I'm trying to calibrate readers' expectations toward what appears to be the average perception, which may be helpful for those who have unusually skewed perceptions of it.
Now, notice I’m not using the word “toned," which isn’t a thing. When people use the word “toned," they’re referring to the combination of (1) being thin enough that muscle definition is visible and (2) having muscles to begin with.
You might not want to get as muscular as the second woman, but getting just halfway there will still make a noticeable difference in your physique.
Women's muscle gain
The limiting factor to how big you can get is the broadness of your skeleton (study). So if your body is on the smaller side (e.g. high school teenager), it will be improbable to reach the same maximum muscle mass as someone much bigger than you. In other words, the average woman will ultimately gain less muscle than the average man.
However, there's research showing that women develop muscle at the same rate as men (study, study, study). (Hat tip to Menno Henselmans for compiling this research.) The difference is that women start with less muscle mass on average and ultimately gain less.
Yes, men have more testosterone, but testosterone is less important to the female muscle development process. In fact, women benefit from higher levels of IGF1 growth hormone, which is critical to muscle growth (study, study).
While there are fewer muscular women in the world, that’s perhaps a reflection of fewer women working to become very muscular. It’s not necessarily a reflection of it being significantly more difficult for women to see progress.
It’s important you understand that you're not at a disadvantage when bodybuilding because thinking otherwise can deter your progress. For example, one study examined the opposite scenario, where men were tricked into thinking they were taking steroids when they weren’t, and they consequently lifted 350% more in weight (study, study)! This suggests your confidence in the gym plays a critical role in how much you can lift.