Here Andrew explains WHY you need to learn this technique, and it's simple, club gear probably doesn't have beat sync. So if you can't do this manually, you're screwed.
No only that, but when songs are analysed by the software, it can and does get it wrong, especially on older 70's 80's 90's songs. 00's and 10's were mastered using computers and have dead accurate BPM's, older music doesn't. That...

If you've never used any hardware, how do you get to know what everything does? To be honest, it's easy, some things you'll use maybe once or twice per session, others you'll use all the time, but you will use everything fairly regularly.
But this is the video you need, and Crossfader will teach you the majority of controls so you can have a play and learn how to learn.