All good information above. When I wanted to switch from spinning reels to BC reels back when I was 15 or 16 years old, bought my first baitcasting reel and read the manual that came with the reel. Set the reel with the spool tension where the lure (practice casting plug) barely falls and hits the ground without the line on the spool to overrun. BTW an 1/4 oz casting plug is pretty light and I would get one 3/8 oz or even 1/2 oz. When I started with my baitcasting reel, I took all the hooks off of a 51 series MirrOLure.
I would set the brake weights with all 6 turned on. Your casting distance with not be very far, but it will be better to cast without backlashes and get the feel for the line coming off the reel during casting (with your thumb). You want to be able to feel the line during the cast with light thumb pressure. You can even feel when the line starts to "fluff up" before a backlash happens and and apply more thumb pressure to stop the reel from backlashing. Don't try to cast far as you are learning, the harder you try to cast, the easier your reel will backlash. Try casting with a smooth casting motion and again don't worry about distance as you are learning.
I'm sure my neighbors thought I was strange as I was practicing on the side of our house as I was learning
As you get more comfortable with using your reel and thumb while casting without getting bird-nest, start turning off your break weights from 6 to 4 and continue practicing until you are getting the hang of the less breaking force with less weights turned on. As you get more comfortable at this setting, then turn off two more break weights from 4 to 2 weights turned on. Continue practicing at this setting. This is the setting that most Shimano baitcasters refer to as the "two break weights turned on and forget it" casting. Once you get this setting figured out, go fishing and have fun. At this point, you can play with the spool tension to get more distance, but the spool will spin a lot faster with the less tension and you will now need to use your "educated thumb" to feather the pressure on the line coming off the spool.
You will still have "professional overruns" occasionally, even with all the practice. Sometimes you will have to cast into the wind and will have to use your thumb more. Try to cast quartering into the wind if possible. Sometimes it's not possible, like fishing the surf and casting with a south wind, casting right into the wind. Use more thumb pressure. Your thumb will be able to tell a great cast and also when the spool is starting to overrun and more pressure needs to be applied to keep from backlashing.
Have fun learning. I haven't bought a spinning reel since I started fishing with baitcasting reels. I can use a spinning reel no problems, but I prefer using baitcasting reels.