I see all these videos online of people playing real time through amp sims and recording a video while playing them. how is this done?

Also, i downloaded some amps sims (Paulin lecto) and it sounds terrible straight through? Is it supposed be like this? I am so confused. I Was looking online and everyon else's sounds so heavy/clear/articulate just crushing.

Is there something I am missing?

Take it easy because I new to this thing! I thought it was as easy as just downloading a good simulator with a good interface (I have sapphire), plug in and go?
Current Gear

Bogner Uberschall
Mesa Dual Rectifier (Old Version)
Orange Closed Back 2x12 Cab with V30's
PRS Custom 24 Top 10 with 57/08 pickups
Schecter Hellraiser
Breedlove Atlas AD20
A bunch of pedals
If LeCto is sounding terrible, I'm 99% sure you haven't got LeCab (or another impulse loader) there with a good impulse on it. It is fairly simple once you get the stuff, it's just that paid simulators include (generally average) impulse loaders with their software so it's a little more plug and play.
If you don't have any impulses, I'd suggest getting at least the 'Sperimental Pack, and then if you're up for it grab the free RedWirez Marshall impulses, Catharsis, and Guitarhacks impulses. If you have all of those you're pretty much set for anything.