That all depends on where you decided to place your jdk.
The default I believe is
At least that is where mine is. What you're going to want to do is add the bin folder in the jdk folder to your path in windows
There are several tutorials online for this. One way of doing it is as such:
Right click on my computer
Go to properties
Click on the Advanced Tab
Click on Environment Variables
Under System Variables there should be something there that says Path
Select it and hit the edit button in this path.
You then want to put the path of the jdk bin folder in your path as such:
Make sure you have the semicolons just like the other path variables. Hit okay, save it, then open up a new command prompt window and you should be able to use javac from the command line.
Let me know if you need anymore help.