Drupal is a bit like the Constitution. It has a strong foundation that is holding up a framework, which is constantly growing. It is unlikely that you will create a site with Drupal and never add functionality to it, or need help, or require updates, and so on, as long as the site is in use.
The following is a list of resources aimed at making the continued use of your site easier.
There are a few different levels of help available. Keep in mind that Drupal is a free product, and as such no one owes you any help. With that said, the Drupal community is large and friendly, and help can easily be found.
If you have a question that doesn't require an immediate response, then you can start by Googling your question (include 'Drupal' in the keywords), or by performing a search at the Drupal web site: drupal.org.
If you cannot find an answer there, or just hate reading 50 articles in the hope that one will be even slightly related to your question, then you can try searching the Drupal forum. If your question hasn't been asked and answered already, then you can post it. The Drupal forum is located at drupal.org/forum.
If you would prefer a more timely response, or think that your question would better be served by a dialog, rather than emails, then you can try the Drupal chat channels. If you have not used IRC (Internet Relay Chat) before, then it might take a little getting used to, but for the most part, it's like being in any chat room, except that everything said is related to the channel name.
You should start by downloading a chat client, such as Chatzilla, which is a free IRC client that ties into Firefox.
Note
The main things to remember when in a technical chat channel:
Don't say 'hi' and wait for a response. Add your question on the same line.
Don't ask if you can ask a question—just ask!
Make your question concise. You can add the details afterwards. You're apt to get more attention if your question is one or two short sentences rather than a long screed.
Don't copy and paste a bunch of code or error messages, etc. If you need to provide that kind of information, then navigate your browser to pastebin.com
(for text) or imagebin.com
(for images) and paste it there. Then copy the link you're given and paste the link in the chat.
Be polite! These people don't 'work for' Drupal. You're asking for 'customer service' from someone who is a knowledgeable product user, not an employee of a company from which you purchased something.
High-priority help comes in the form of paid assistance. There is a plethora of knowledgeable Drupal developers out there, but please, please, please don't let someone you don't know touch your site. Use a consulting company with a good reputation, such as AyenDesigns.com. Get references and check them, or use a moderated job site, such as Elance.com orRentacoder.com, to obtain assistance. If you use your cousin's friend who's good with computers, then you're asking for what you get.
Note
ALWAYS make a complete backup of your web site and the database before letting someone touch it. Don't rely on the web hoster's backup. If your site gets trashed because you let your cousin's friend 'fix' it, then the web hoster will probably charge you a hefty fee to restore it from their backup.