It is true that you can hold a FL ID card and a DL from another state,
The FL ID card looks and acts the same as a DL but only in the state of FL. This is for people who spend part of the year in FL and part somewhere else. They are usually referred to as "snowbirds".
It is useful for getting FL resident discounts and cashing checks etc.
When applying for a FL ID...you must show a valid driver's license, another form of ID and proof of residency (ex...tax bill, phone bill, voter's registartion etc...)
It is also NOT easy to get. FL used to allow folks to get them in the back of Eckerd's drugstore, which I where I originally got mine. That has changed, You now must get one at the DMV which does take appts (usually weeks to months in advance) as well as walk-ins......which can take the majority of a day.
You must take an eye test, sign a few forms and pay $20.