You need to get the fly to a fish in a way that doesn't spook the fish. If you got your line right the rest is in accuracy and technique. You just need a lot of practice with the right technique to get accuracy.
There are quite a few different casts. Overhead, roll, reach, backhand, tuck, and the list goes on. To start with you need to get the overhead cast down.
All fly-fishing casts have a back-and-forth motion to it. It takes timing, or rhythm. Be gentle, no whip cracking.
Start by bringing the line from in front of you to behind you.
Raise the rod from horizontal to vertical.
When it's up, wait for the line to start to get slack then Drop it back down into horizontal.
Aim towards your target. Repeat this until you reach it. Just take your time.
The last thing you want is to spook the fish. Be gentle until it's time to not be gentle.
So, there you go. The basic cast. After you get that down it'll be time to start moving into some other ones. They all have a place and time to use. "For there is a proper time and procedure for every matter". Ecclesiastes 8:6.