The field name is the name of the field. Field type is the storage form of field content. The field length is the length that the field can hold. A long integer is a long numeric form without a decimal point. Double precision is a kind of floating-point type, which is simply a long number with decimal point. The length of the field depends on your requirements, such as how many decimal places you want for double precision type and how many words you want to write for string type.