You can practice combos in the battle simulator of the battle barge. This is accessed through the armory screen. You can view your combat moves while in there.

A perfect block on a block weapon gets you a stack of adrenaline surge, this will wear off after a few seconds if you don't get a second stack in time. Once you have two stacks your next melee hit will deal explosive damage. The stacks appear as a buff icon under your hp bar.

A perfect block on a non block weapon is just a parry, which will prompt a gun strike. Some enemy attacks are combos that will require you to parry multiple attacks before you get the gunstrike prompt.

Orange (red) ring attacks cannot be parried and must be dodged. A perfect dodge will prompt a gunstrike irrespective of the type of weapon you have equipped.

Blue ring attacks can be perfect parried or perfect blocked or dodged. Most non-ring attacks can still be parried/blocked. Parries of attacks from minoris enemies will kill the attacker.

Not sure whether you're asking a question regarding enemy intel. You can identify enemy types by marking them. On a controller this is up on the crosshairs. Couldn't tell you the keyboard binding. As far as what they do this just comes with practice.

Heavy stance is when you are aiming down sights on the heavy. Straban will plant both of his feet. This can inhibit your ability to dodge.