Those differences are small compared to what you lose by running the mixer into the red or using crappy speakers or amps.
The OP was new, so I’m assuming he hasn’t sprung for good monitors yet. I don’t think you’ll ever hear the difference between sound cards on computer speakers.
On big systems, it depends on how good they are…I’ve heard club systems where you couldn’t tell the difference between vinyl and ringtones.
Yeah no monitors yet but i have two amps and speakers im gonna use.
The most obvious advantage of using a sound card with more than 1 stereo out is that you can headphone cue- one of the most useful tools available with a dj. Without it you can’t really beat match unless the tracks are the same bpm and you have no way of listening to the track before the audience hears it, so if it’s shit you can’t really go back.
Get a soundcard dude.
download the latest asio4all drivers from here http://www.asio4all.com/
as you are using the internal soundcard from your computer this will be your best option till you get a soundcard.
Working on it right now sir 
+1
Oh yeah, it’s better. But it’s not necessary for the first stages of learning. And you can always mix in mono…it’s early on the list, but it’s not first.
Yeah, sorry, just responded to the blanket statement.