Once you have possession of any CannaCard, you may do whatever you like with it (even destroying it).
Within paintswap, navigate to the "NFTs" section under the profile icon in the top right orner. From there, you will be presented with a number of ownership options.
To sell your CannaCard on the open market for anyone to buy, simply select the "list" option. This will present you with a simple listing process, which will let you customize a number of options, including the price you would like to sell your CannaCard at.