If you have even a basic understanding of music composition, you'd benefit from using a DAW in order to compose music. What is said about DAWs not requiring any prior musical knowledge is correct in that it is easy to make a sound and it is easy to layer it on top of other sounds, and it is easy to sequence them together until you have something that's track-worthy. However, this doesn't mean that they are so abstracted that someone as a musician or composer would not be able to utilize them.
In my experience with FL Studio (as it is my DAW of choice), I find that my prior musical knowledge, of rhythms, notes, harmonies, and so on, make it easier to navigate and get accomplished what I'm hoping to do. This is also augmented if you have a MIDI keyboard and are able to record your playing into the DAW to lay down a sequence. I spend a lot of time in the Piano Roll in FL Studio getting melodies and harmonies assigned to individual instruments, then I layer them on top of each other and set automation values to get my desired results.
One big important thing to keep in mind is that you'll need to venture into the world of VSTs a good amount to be able to make music solely out of a DAW install. FL Studio comes prepackaged with some simple VSTs that will allow you to get your feet wet, but depending on the style of composition you'd like to develop, you'll want to hunt around for the VSTs that give you the sound you want (for example, if your aim is EDM, z3ta+ is common, as is reFX's Nexus. You could look at Miroslav's Philharmonik as a good starter for orchestral instruments, as well, though there are probably better.)
Lastly, the fast way to bridge the gap between a DAW and engraving software like Sibelius is to understand the corollaries. For example, a track in a DAW is like an individual instrument in the score. You assign a VST or Sample to this track, and then use the piano roll to decide at what time (which measure, beat, etc.), for how long, and which note. That's sort of like putting down the notation. You can then map these tracks to mixer i/o tracks, in order to control their gain, panning, and other effects, and apply effects to them. This is sort of like applying dynamics and other style markings in written notation.
EDIT: Forgot to mention: FL Studio comes as a demo (in which you can't save your work), but should give you full enough functionality to try out and see if it works for you. There are different DAWs for different ways of conceptualizing the idea of music composition in software. Check a few of them out this way before committing and see if you can find one that matches your style.
