I'm fairly new to fishing. I have always used spinning reels for all of my fishing. I was wondering what the differences are in a spinning vs. baitcasting reel is. Such as, why one would choose to use a baitcasting? And when to use one over the other.

Just curiosity.

There is more control with a b/c just stop the spool plus you can turn against the drag and no line twist to deal with JMHO

They give you much more flexibility in casting - you can cast your normal sidearm or overhead and then control the distance exactly as mentioned. However you can also backhand cast it (like a sidearm pitch), you can pitch it, and you can flip it. When you start getting good with one, the versatility is so much greater over spinning it is amazing.

You should be able to learn any type of cast, and be accurate with either.  You can also control a spinning rod by feathering the line with your finger.

Where a baitcaster will shine is in the way it handles heavier baits and heavier lines.  Speaking of line, there virtually no line twist with baitcasting gear.

I think there is also an advantage in the velocity of the bait when cast, especially on windy days.  Modern baitcasting reels have superb braking systems, and once set up right for the bait and conditions, you can really whip a bait so it cuts through the wind and hits your target.

The last advantage is more a personal preference.  I find a casting rig much more comfortable in regards to hand and arm position for a day of fishing.  you're hands are both at about the same level, keeping you shoulders and back in better alignment.  With spinning gear, you cranking side is always haunched a bit.

A couple simple rules of thumb (not gospel):

Line <= 8# diameter: use a spinning reel, any heavier, go with a baitcaster.

Baits <= about 1/4 or 3/8 oz.: use a a spinning reel, 3/8 and heavier, use a baitcaster.

There are exceptions, but it usually requires specialized gear.

Thanks for the help. I have just seen a lot of people using them, and I just wanted to know the differences.

While I would agree you can perform any cast, to some extent, with a spinning reel that you can with a baitcaster, the idea that you can perform them as well is silly.  The control you have over the spool is simply unmatched compared to working the line itself on a spinning reel.  The key here is "to some extent".