If you own a card, you are able to rent it out via the Splinterlands website or third-party websites. This article describes how it's done on the Splinterlands website. This guide assumes you are already logged in.
Step 1: Click on "Cards" in the top bar and select the card you want to rent out (click on the check box next to the card). After that click on the house-shaped icon located at the upper-right.
Step 2: Make sure that you have selected the "Rent Card" tab. Below that fill in the price. Then press "Rent".
Note: Renting out below the "Suggested price" will increase the chances for the card to be rented sooner and also be rented again to a new player, after the first rental period has ended.
Step 3: Double-check the price and confirm
The card is now for rent, you can recognize this by the icon of the house next to the card.
If you see both the icons of the house and the arrows lit up next to the card, this means the card is rented out to a player
To view the recent history of your rentals (including income) click on the "Market" tab, then on the "Card Rentals" and finally on the "Activity" tab.
It's also possible to rent cards from other players.