All art submissions appear instantaneously on your user page and search.
If you check the box to include your art in the Art Portal, it will be included in the Art Portal galleries, IF you have been scouted by a member of the community.
To be scouted, you must upload at least four pieces of work, at which point existing members of the art community have the ability to send you invites. The invite will appear in your inbox and you must accept it to complete the process.
Once scouted, you will have the ability to scout others. Artists CAN lose this ability if they exercise poor judgment. Artists can also be de-scouted if they submit bad art, and can be permanently banned if they break the rules.
This is explained in much better detail in Ornery's Handy Dandy Scouting Guide.