If you ran the wizard, then it is almost certainly the case that you already added an owner user for yourself. If not, however, you can add one via the handy-dandy supybot-adduser script. You'll want to run it while the bot is not running (otherwise it could overwrite supybot-adduser's changes to your user database before you get a chance to reload them). Just follow the prompts, and when it asks if you want to give the user any capabilities, say yes and then give yourself the owner capability, restart the bot and you'll be ready to load some plugins!

Now, in order for the bot to recognize you as your owner user, you'll have to identify with the bot. Open up a query window in your irc client (/query should do it; if not, just know that you can't identify in a channel because it requires sending your password to the bot). Then type this:

  help identify

And follow the instructions; the command you send will probably look like this, with myowneruser and myuserpassword replaced:

  identify myowneruser myuserpassword

The bot will tell you that The operation succeeded if you got the right name and password. Now that you're identified, you can do anything that requires any privilege: that includes all the commands in the Owner and Admin plugins, which you may want to take a look at (using the list and help commands, of course). One command in particular that you might want to use (it's from the User plugin) is the hostmask add command: it lets you add a hostmask to your user record so the bot recognizes you by your hostmask instead of requiring you always to identify with it before it recognizes you. Use the help command to see how this command works. Here's how I often use it:

  hostmask add myuser [hostmask] mypassword

You may not have seen that [hostmask] syntax before. Supybot allows nested commands, which means that any command's output can be nested as an argument to another command. The hostmask command from the Misc plugin returns the hostmask of a given nick, but if given no arguments, it returns the hostmask of the person giving the command. So the command above adds the hostmask I'm currently using to my user's list of recognized hostmasks. I'm only required to give mypassword if I'm not already identified with the bot.