How does it works?
Margin loans. Essentially, you're lending to short sellers.
Can you explain a bit more to a newbie and what is the minimum?
I'm afraid I don't know the minimum, but I can explain the loan market. Poloniex now allows short selling for certain high-volume coins. A short sale, or forward sale, consists of borrowing someone's coins, selling them on the market, buying them back later and paying back the loan. This technique is only profitable if the coin drops, allowing the short seller to buy-back his borrow at a low enough price to pay the interest and leave him with a profit.
Just as the object of a trading purchase is to buy low and sell high, the object of a short sale is to sell high and buy low.
If you loan your DOGEs in that loan market, you're offering a short seller the use of your DOGEs for a time at the agreed-upon rate of interest. They'll be sold and the short seller will pay you back + interest when he buys back the coins he borrowed from you ("covers his short") Interestingly, the lender to a short seller is essentially making a bullish bet. If the shorter loses by "selling high and buying back higher", the lender get the interest plus a capital gain. But on the other hand, a successful shorter pays back coins that are worth less.