Have you installed Lazarus or only the FPC. The FPC is the compiler, while Lazarus is an IDE (Integrated development environment that contains an editor, can call the compiler, use a debugger and all the stuff you need).
I would recommend using Lazarus and not plain FPC.
If you Installed lazarus it is rather easy: Start Lazarus (probably somewhere in your start menu)
Now you should see a bunch of windows, amongst others a bar on the top containing a lot of icons, a WYSIWYG form editor (a Window called Form1 with dots on it) and a source code editor.
I would recommend first to get into the basics without the GUI stuff, for this simply go to (in the menu) File->New and select Program. Now a new Lazarus project should open with one Main Pascal File in the editor.
In the up most window there is a little green arrow button, use this to compile your code and start your application.
Thats the core basics, now you can start hacking