Several CSS gradient generators are available online. They can help you make gradients as you're learning how gradients work.
Websites
CSSGradient.io offers a simple interface for exploring gradients. It doesn't include every feature (e.g. conic gradients), but it has some of the ones you're most likely to use.
GradientCSS.org has a few more options. It's visually simpler.
Sonjukta CSS Gradient Generator
The Sonjukta CSS gradient generator features sliders and other tools to help you design a gradient. Here are some images:
