For face-to-face games:

• Meetup.com
• Obsidian Portal
• Ask on Reddit's Looking For Games subreddit

For play-by-post, the following is adapted and expanded from a post by Peter Seckler on http://rpg.stackexchange.com:

• Enworld has Play By Post available at http://www.enworld.org/forum/playing-game/
• The RPG Site has Play by Post available at http://www.therpgsite.com/forumdisplay.php?f=26
• Something Awful forums has the most lively Play By post forum I've ever seen at http://forums.somethingawful.com/forumdisplay.php?forumid=103

Even smaller boards often have play-by-post. Other tools:

• http://iplay4e.com for hosting character sheets
• http://catchyourhare.com/diceroller/ for online dice rolling
• http://wikidot.com for campaign documents and sharing
• http://Zoho.com
• http://epicwords.com

In general, talk over the sort of character that the player wants to play, and the genre of story (investigative, action, adventure, etc.). Start the character in a constrained environment; a village rather than a city. Start with skill checks; you can spend most of a session just exploring the environment. Then start a fight with one simple creature, like a dire rat or a fire beetle. Work up from there.

The Iron Lords of Zekesh is a short one-on-one D&D 5E campaign posted on YouTube, where you can see how this is handled in play.

https://dmsguild.com

http://www.livingforgottenrealms.com/adventures.html

http://www.dungeonmastering.com/campaigns-adventures/83-free-dd-adventures

http://livingfree.wikidot.com/list-of-libre-games

About 17 black-and-white monster illustrations: http://www.therpgsite.com/forums/showthread.php?p=191851#post191851

60 Terrible Character Portraits for Creative Commons Release (actually not so terrible): http://www.kickstarter.com/projects/mungo/60-terrible-character-portraits-for-creative-commo

Various old, black-and-white sci-fi and Greek-style fantasy drawings in the public domain: http://public-domain.zorger.com/

http://www.fantasy-art-workshop.com/fantasy-art-landscapes.html

http://imagespublicdomain.wordpress.com/2010/11/13/dragons/

Some beautiful old comic book illustrations: http://goldenagecomicbookstories.blogspot.com/2012/01/frank-godwin-1888-1959-blue-fairy-book.html

You can also search Flickr, turning on the Creative Commons options at the bottom.