That's great advice from Charlotte Rose.
I would recommend that you spend some time finding out about how the profession works (and also finding out about amateur and youth theatre opportunities). This will really help you to work out where to look for information and should mean that you are less likely to waste time or money on false promises.
Most auditions do go through agents, as Charlotte Rose says. Getting an agent isn't easy and once you have an agent there is no guarantee of getting called in for auditions in any case - it's a very overcrowded world! Most professional theatre jobs will go to older performers who look young. TV and film work will tend to go to those with some experience.
The reason you find it hard to find out information about auditions for professional work is because this information is rarely in the public domain. This site is a good place to look for information and Screen Terrier, Talent Circle and Mandy are other possibilities (Talent Circle and Mandy will mostly be unpaid work, student films etc).
I recommend reading some or all of these books which will tell you a lot more about agents, casting directors, how to prepare for auditions, training etc etc. The more knowledge you have, the better you are likely to do! Any local, amateur experience is well worth looking at too.
An Actor's Guide to Getting Work - Simon Dunmore
So You Want to Tread the Boards? - Jennifer Reischel
Make Acting Work - Chrys Salt
Actors Yearbook
Contacts
www.ncdt.co.uk is another useful website if you are considering trying to make acting your career.
