You can attack twice, instead of once, whenever you take the Attack action on your turn. Moreover, you can cast one of your Wizard cantrips that has a casting time of an action in place of one of those attacks.
Extra Attack
Raw data
{
"name": "Extra Attack",
"page": 27,
"level": 6,
"__prop": "subclassFeature",
"header": 2,
"source": "FRHoF",
"entries": [
"You can attack twice, instead of once, whenever you take the {@action Attack|XPHB} action on your turn. Moreover, you can cast {@filter one of your Wizard cantrips that has a casting time of an action|spells|level=0|class=wizard|cast time=action} in place of one of those attacks."
],
"className": "Wizard",
"classSource": "XPHB",
"subclassSource": "FRHoF",
"subclassShortName": "Bladesinger"
}