The best advice to be given to anyone wishing to start dinghy sailing is to take your time, don't rush into anything and don't try running before you can walk.
First thing to do is to read around the subject and at least gain a basic understanding of what is involved in owning and buying a sailing dinghy, what the parts of a dinghy are called etc. The Internet is an ideal place to do such research and this will be of great help when you start learning to sail.
Next locate the sailing clubs in your area and visit them. Get a feel for each one. Ask yourself
What are the members like ?
Were you given advice ?
Were you made to feel welcome ?
Do they offer any sort of training ?
What sort of boats do they sail and at what times ?
Unfortunately many clubs forget about attracting new members and concentrate solely on racing without realising everyone has to start somewhere. Gone are the days when all sailing clubs had waiting lists of people to join. Many clubs are now beginning to realise they must activley seek new members to maintain numbers and in some cases survive. These clubs are beginning to offer training courses for beginners.
Don't rush into buying a boat. Most clubs usually have a few boats which members can use. Take advantage of this fact until you have more knowledge about dinghies and have decided if sailing is for you.
When you eventually get to the stage of buying a boat you should have a good idea about what you should be looking for. It's easy to waste money buying a boat that may be no good. A good place to buy a boat is at your local club. People constantly trade up so boats regulary come up for sale. The best thing about buying a boat from your own club is that often people will know its history.