How do you use exposure in portrait photography (I'm confused of exposure for portrait)?

I need a bit of help in exposure, and I'm still confused about it. Recently, I bought a 50mm F/1.4 lens for portrait photography, and I'm happy with it. Although, when I was testing it, I keep getting these dark shots because the aperture is low, and these blurry shots because the shutter speed is too slow. Whenever I adjust it, I can either choose a kinda blurry shot w/ perfect lighting, or a kinda dark shot w/ no blurs. Could you explain this a bit more, or any tips and tricks I can use, websites.