First thing, download Bitcoin Lightning Wallet (BLW), the best wallet on the market. There are others, but no other non-custodial alternative is so well-supported, light, fast and filled with cutting-edge technology as this.
Get a channel on lnbig.com (yes, they will give you a free channel, watch the video to see how to do it -- and remember to ask for the smallest possible channel size):
Now that you have a channel up you can start filling it with your coins that are currently in an on-chain normal Bitcoin wallet. The first 20000-ish satoshis will be reserved because of an idiosyncratic requirement of current Lightning Network channels (they demand a 1% "deposit" to be kept on each side of the channel so cheaters can be punished if they ever try to break the protocol, but you'll get them back if you later decide to close the channel), so you'll have to deposit a little more than that.
Visit https://charger.alhur.es/ on a desktop. Scan the QR code with your BLW wallet (swipe from right to left to open the scanner) and follow the instructions. Send bitcoins to the address given there and wait until it's confirmed. Come back to the page later, scan the QR code again to login and withdraw your satoshis. You are now on Lightning -- and charged!
If you want to confirm everything is working you can play poker against others at lightning-poker.com, show your sports' knowledge by betting on microbet.fun or buy some lightning.gifts for your friends (be sure to show them this guide first).
If you want to earn some easy sats there's also a plenty to be earned. There's some tips on how to do it in this other guide.