Someone posted a helpful answer to one of my questions. Now I want to contact that person. How can I do this? Can I send a direct email?
If they do not supply contact information in their profile, then you cannot contact them privately through this site. SE does not work that way. We respect our users' wishes to remain private.
If you think there is an emergency--for instance, if a user might inadvertently have posted sensitive information and you wish to warn them--then please just flag their post for moderator attention. When you raise the flag you will be able to explain the reason.
No (unless you happen to find him in chat). Only moderators can contact people via e-mail. For fuller explanation, see this: How do I contact other users? (meta-SO) and this: How to contact a user? (meta-Cross Validated).
P.S. I find the auto-suggest option while asking a question incredibly useful; think it is worth it to pay attention to the list of "Questions that may already have your answer" during typing - although it may take a few seconds for the script to catch up.