my $column = ( $type eq 'alpha' ) ? 'name' : "CONCAT_WS(' ',keywords,category)";

It's just a compact way to write if (..) {} else {}. Look for Ternary "?:" in perlop.

my $query = "SELECT name, address, city, phone FROM valley ". "WHERE $column LIKE ? ORDER BY name LIMIT ?,?";

The concept of Placeholders and Bind Values is fairly well described in the DBI documentation.