an eyelash curler really isn't as scary as you might think. But just keep in mind that not every curler is fit for every eye. The curvature of your eyelid, and the width of your eyelid can affect how easy you fit into some curlers.
Just place the lashes through the little hole, and squeeze. Squeeze slowly to make sure you don't pinch, and once you know you're squeezing, you can press tighter.
Think of like pinching your skin on your arm. If you go slow and stop when you realize you're pinching enough for pain, it really doesn't hurt much -- if you pinch fast then it's kind of too late to stop the pinch and it makes you jump. You can always stop squeezing the curler and replace, resqueeze as soon as you realize you've got skin instead of just lashes!