The string concatenation operator is two vertical bars: ||
Note that if you want to concatenate a number you have to convert it to a character string first, using the CHAR() function. So your example would be:
char(year(column_name)) || "-" || char(floor(field_name))
If your table has columns called column_name and field_name, then a column formula would be:
char(year(:column_name)) || "-" || char(floor(:field_name))