It's not that hard mate to be honest. You just need to get your head around the parallel timing of stuff, overlaying music etc. Other than that it's just getting the timing right.
Start off with something simple like Lt_Swan - dazed and confused
, as he laughs in the face of an I.E.D.
Well, I [censored] myself at least!
Simply add three clips in order. Your chosen intro, the clip containing the footage you want, and then your chosen outro. Highlight the part of the clip you want and then add the slo-mo effect.
Once you understand those basics, you can then move the speed up and down for the fast forward effect, and add music layers as you wish. Again the only patience required is getting the timing right, which is how you end up with something like this
On the BF1 clip for example, timing the end of your intro, perfectly to the instant that you spawn into the game from the in game lobby, gives you a really professional looking transistion
free of charge.