Let me echo what others have said about
learning on a sailing
dinghy. I learned on an 18 foot Flying Scot, and have since then have moved "down" to 14- and 15-footers for pure sailing pleasure.
In a
dinghy, everything one does counts: sail trim, balance, how you take a wave, reading the
wind off the
water, playing gusts and lulls, and on and on. Sail a dinghy a few times and you will know from experience that if you do X the result will be Y and if you don't do it quite right you may find yourself righting a capsized boat

Which you will anyway, since the only person who hasn't capsized a dinghy is the person who has never sailed a dinghy.
Once you move into larger boats, you will find they respond to the same forces, and react the same way as a dinghy, just much slower and more subtly. You can be doing something wrong in a big boat for a long time before realizing it. But the person who starts out dinghy sailing develops a second sense for sailing the larger boat well.
Having said that, it's also good to have some theoretical knowledge before you start sailing your dinghy. Best way is to find a
sailing school that will give you the basics, some will do it in a concentrated weekend course. Then it's just a matter of sailing to really learn what you've been taught.