Dude, where to start? Theres so many knobs and levels to adjust in massive I doubt the person who wrote the program knows how to use it fully. It good tho coz u can pretty much create any sound u want if you try hard enough.
OK, a couple of quick tips;
Most drum and bass the bass sound will uses Saw waves. You'll nearly always set Osc 1 to Square Saw, and choose which ever other ones sound nice for Osc 2 or 3. I usually only use 2.
You will always want to detune the bass a bit to make it wider, which can be done in the "voicing" section by pressing the button by pitch cutoff that says 'off', and then sliding the level aboout 1/4 - 1/8 of the way along.
Also in voicing on the left is the unisono, which should go up to 2-4 to make it sound fatter.
And just piss about with the presets on filter one and filter two, add some distortion to the bass using the inserts at the bottom (you need to do some routing to get this to work best) and create some banging LFO's. You'll always want to use the performance LFO setting, as you can make your own LFO rhythms and stuff with that.
And of course, read the instruction manual. Only takes a couple of hours and you'll have mastered the basics.