It's said that knowledge is power, and the most powerful thing you can do for these lions right now is learn about their plight.
Born in "lion farms," baby lions are raised by vacationing volunteers who often don't know the bloody end that awaits these cubs. Meanwhile, all across the world (although mostly in the U.S.) people go online, look at images of lions ripe for being hunted, and when they find one whose head they'd like to hang on their wall, they place their order and pay thousands of dollars.
These clients then travel to these facilities, which largely exist in South Africa (though the U.S. is home to many of these places as well). Once there, the clients are given guns and escorted out into a small enclosure where their lion has been corralled. Sometimes the lion is drugged to make him - the target - easier to shoot.
This is what's known as "canned hunting."