Home > Append Queries stacks the rows of one query under another: March's orders, then April's. Merge adds columns from another table; append adds rows.
Columns are matched by name, not position. A column that exists in only one of the queries is kept, with nulls for the rows from the other, so check that both files use the same headers before you append.
Clean each source first (or reference cleaned queries), then append: the combined query inherits whatever state the inputs are in.