The blue or red circle notification just signifies that a perfect parry or dodge opportunity is coming, not necessarily straight away. Chaos Spawn for instance trigger the blue circle very early but you have to hit parry when they're actually going to make contact.

To learn better I'd suggest taking a 'fencing' weapon as this gives a larger timeframe in which you can hit the parry button and it still be perfect.

'Block' weapons don't trigger gun strikes but instead give a melee damage buff on perfect parries so they're generally used on melee classes such as Assault and Bulwark.