When starting out in FL studio the hardest thing to get is a melody. Drum kits make the back beat very easy to create and tweak, but without a catchy or mezmorizing melody your song will flop. The easiest way i've found to make a melody is in the riff machine.
The riff machine has many controls and will randoly place notes together, allowing you to edit and splice them to your delight. To use the riff machine, click the upper left arrow in the paino roll, go down to tools, then riff machine. You can click roll dice which will randomly roll all options, or you can do one at a time. Be sure to click ok and not just "x" out.
Awesome, you have a melody. Tweak all the bugs in it, and presto you're on your way.