Curly braces build an array right in a formula, and it spills like any other array result. In the US-style locale a comma starts the next column and a semicolon starts the next row: ={1, 2, 3} is one row, ={1; 2; 3} one column.
The pieces can be ranges, which makes braces the quick way to rearrange data:
={A2:A11, C2:C11} puts two columns side by side, skipping the one between.={Jan!A2:B6; Feb!A2:B6} stacks two ranges, one under the other.={"Player", "Points"; A2:B11} puts a header row on top.
Every piece must fit: stacked ranges need the same number of columns, side-by-side ranges the same number of rows. Otherwise Sheets returns #VALUE! and says which side is short.
SEQUENCE(rows, columns, start, step) generates numbers: SEQUENCE(10) is 1 to 10 down a column. With a date as the start it lists consecutive days.