Insertion is the operation of creating a new table from an old table by adding a row. SQL databases perform this operation in place, so the new row is added to the existing table:
insert into ITEM values (4, 'Fum', 45.0)

should be

Insertion is the operation of creating a new record from an old table by adding a row. SQL databases perform this operation in place, so the new row is added to the existing table:
insert into ITEM values (4, 'Fum', 45.0)

No, a relvar is a variable with a time-varying value and adding a tuple to a relvar effectively creates a new value that is assigned to that variable. If you don't understand this, read the next sentence in the book which explains the situation in SQL.