Let's start with the most common verb form of "lead": It's pronounced leed, with a long e, and it means, more or less, "to guide," "to direct," or "to be first." So far so good. Its past tense is "led," pronounced with a short e. So, "lead"=present, "led"=past. Sounds easy, right?
The reason this gets confusing is that "lead" can also be a noun. With a long e it means "the person in front" or "leash" or "the first card played" or "the distance a base runner is from the base," as well as some others. But it can also be pronounced with a short e, in which case it's the metal that's in a pencil. (Or was, before lead poisoning, but anyway.) So because "lead" can properly be pronounced with a short e, it's easy to think that that's how the past tense of the verb is spelled--but it's not.
Harry leads his year in detentions
Jack has led SG-1 into some interesting situations.
The lead in my pencil needs sharpening.
Why isn't your dog on a lead?
You can lead a horse to water, but you can't make him drink.
Jim led Blair to the temple.
You Can Lead A Horse To Water, But You Can't Make It Drink ( you can show people how do do things, but people must help themselves ... )
(proverb) says that you can give people what they need to help themselves, but you can't force them to do it; people need to help themselves. Example: "I told her exactly what to do, but she didn't listen to me." Reply: "You can lead a horse to water, but you can't make it drink."