At first, you must to have atleast steam level 10, to put an artwork showcase to your profile.
Go to your profile and choose "Artwork" section.
Click on "upload" button.
Then now choose one of this artworks:
Go to your profile and click "Edit Profile" button.
Scroll down to showcases sections and choose "Artwork Showcase"
Then click on it and choose needful artwork.
All done! Now all of your friends think that you have a lot of expensive items!