you select data from a SQL database using the
SELECT statement
you can limit the the data returned by the SELECT statement by using a WHERE clause
you can retrievve the data form more than one table using either a JOIN clause or a WHERE clause, of the two the JOIN is probably the better one to learn, although the WHERE clause can be easier to form for beginners.
SQL can perform all manner of mathmatical and and string operations. it was designed to be legible to English speakers
SELECT my, comma, separated, columns, from MyTable
join AnotherTable on Anotherable.Column=MyTable.column
where acolumn < aNumber
OR
SELECT my, comma, separated, columns from MyTable, AnotherTable
where acolumn < aNumber and Anotherable.Column=MyTable.column
SELECT ((columna * 1.05) + (columnb * 1.175)) as myNewValue from MyTable