“Edit / Delete” button for each row & header column is ‘Action’ in the md-table component

You are on the right track, you just need to add an actions item to displayedColumns list:

    displayedColumns = ["username", "email", "userFirstName" ...  , "actions"];

and:

    <ng-container cdkColumnDef="actions">
        <md-header-cell > Actions </md-header-cell>
        <md-cell *cdkCellDef="let row" >
             <button md-raised-button >Edit</button> 
        </md-cell>
    </ng-container>