I happen to have FL Studio 6, and I've learned a couple of things about it through experimentation. I'm not going to claim to know anything about FL beyond the very basics, but I'll try to tell you the few things I've figured out.
Please note that this is for FLS 6; I don't think they're too different, but there's a chance that none of this will work on 7.
When you open FL Studio, you should see a window with a stripped-down percussion section on it. In my version, this consists of the effects "Kick," "Clap," "HiHat," and "Snare." If you don't see anything like this, then go to "File -> Templates" and select something from the options there to get a drum kit.
Now, you see the boxes next to each of the instrument names? Those are used to create percussion for your song. Click on a row of boxes to light them up. Now if you hit the "Play" button at the top of the screen, you should hear... well, a bunch of noise. If you play around with this, you'll be able to make a good drum loop.
Having done this, you'll obviously want an actual instrument to play. Go to "Channels -> Add One" and select an instrument. I'll use FL Keys, a piano/organ simulator, for this example.
A new icon, labeled "Keys," should appear in the Step Sequencer, where the percussion instruments are. Now, you can program the new channel like you did the drums, but this will only let you use one note, and I'm sure you're not into
that kind of music. Instead, right-click on "Keys" and select "Piano roll" from the menu.
This brings up the Piano Roll box, which is where the actual music begins. The piano roll displays note pitch vertically and duration horizontally. It's already divided into measures, which are marked by light lines with numbers at the top. Click the Draw icon in the upper-left corner (it looks like a pencil). Now if you click on the grid, you can place green bars, which represent music notes, onto the roll. You can extend their duration by clicking on their right side and dragging them out. To make them automatically extend by certain intervals (helpful when you want to edit music quickly and cleanly), click the "Snap to grid" icon (looks like a grid) and select an intervals like "1/2 step" or "Step."
At this point, if you hit the "Play" button, whatever notes you've put in the roll will play on top of your drum sequence. By default, the sequence won't continuously replay if the piano part is onger than the percussion part; you can change this by clicking the "Repeat step sequencer" option in the upper-left corner of the step sequencer.
I'm assuming that you know your way around a music keyboard, so do what I've noticed you do particularly well and go crazy. Check out the other channels; FL Slayer, for example, simulates a guitar, while Wasp, with a little teaking, sounds exactly like an Atari 2600. (To edit a channel's "sound," just click on its name in the step sequencer. This brings up the sound plugin's menu, which lets you rework the sound as much as you like.)
This is all very basic, of course, but I can't do anything better. I hope that FLS 7 isn't too different from 6 and this mini-guide proves helpful. Here are some links to songs I've programmed with FLS 6, if you want to examine them and see how they work:
http://kyunji.fateback.com/media/asdffdsa.flphttp://kyunji.fateback.com/media/Battle%201%20--%20COMPLEAT%20(manual%20repeat)%20(2).flphttp://kyunji.fateback.com/media/Battle%201%20(Crono%20Trigger)_2.flp