Okay, so I'm invading systems and it gives me different options for invasion. The "blitz" one gives me more rounds but less health on my troops. Anyone wanna explain to me what the rounds are? Thanks for the help!

Rounds are how many times your ground troops will attack.

Blitz would cause a total amount of attacks (Rounds) 4 times VS 2 times in other choice.

 So the idea is if you have the bigger force by at least 30-40% then go with Blitz.

If your army is the same size or a tad bit bigger or even way smaller. Then go with the 50% extra HP choice. 

Basically do you want to try to take the system is a short time span? or save your troops at the cost of time?

I do not recommend the 3rd choice, as it's a bit hard to determine when's the best time to use it. Unless you want to be a A-hole and kill some pops or raze some buildings.

Be careful how many systems you invade as there is currently no way to choose to own the system or not and soon you'll find yourself getting a -50 in disapproval due to over colony modifiers.  

Using privateer action will allow you to destory a sustem without taking it. Useful when you are up against the cap or just dont want a crappy system... perticularly craver depleted ones.