@JustNatsuki
Evasion is one of the most important mechanics in the Fire Emblem games.
Unlike Heroes, which is all about Attack and Defense (and Speed), the main Fire Emblem games also have Accuracy and Evasion.
Some tiles improve a character's evasion rate, most commonly the Forest tile. Fire Emblem veterans usually position their characters on Forest tiles expecting them to be harder to hit, but there is no hit/dodge mechanic in Heroes.
Dual Attack is a mechanic introduced in Awakening, which carried over to Fates.
When 2 units are standing next to each other, both units will attack together. The other unit can still move afterwards, so Dual Attack increases the damage you can deal.
Capture is a mechanic from Thracia 776 that reappeared in Fates.
It allows your units to capture an enemy unit. You can then steal their items or force them to join your army.
Dragon Vein is a mechanic from Fates.
There are special "Dragon Vein" points on the map, which affect the map when activated.
Basically, Summoner is saying that Heroes is lacking in basic features.
If you like Heroes, you should play the real Fire Emblem games. Heroes is like a small drop of Fire Emblem diluted in tons of water.