In my dialect of american english, you fill out the form by filling in the blanks on the form.
Videos of Fill In A Language:En
fill in and fill out are the most widely used phrases to convey that meaning. I wonder if any native speakers use fill up in every day english for such purpose.
To put something into (a container, for example) to capacity or to a desired level fill a glass with milk filled the tub with water.
Your will lets you decide what happens to your money, property and possessions after your death.
When accompanying a song, the instrumental line usually follows the vocal line in unison with some ornamental variation and fill-in melodies between vocal phrases.