The 4 "H's" stand for head heart hands and health. Its an agricultural club in the US and can be for anything from horses to hogs. I was in it in high school so its been a few years ago
I think its mainly for school age kids. Not sure exactly the age's when you can start. Here is the 4-H pledge
"I pledge my head to clearer thinking,
my heart to greater loyalty,
my hands to larger service
and my health to better living,
for my club, my community, my country, and my world."
Hope this answers your question. Its basicly a farm club.