Fillwords is an educational word-puzzle game with a drawing element. The player links together letter tiles on a playfield level by level to unlock different types of elements and lifeforms that are part of the evolution of the ecosystems on Earth and even the human race. The player receives opportunities to learn about the wide diversity of life on the planet. Peaceful, repetitive popping sounds like popular pop-it games make gameplay relaxing and fun.
Each level offers the player a number of letter tiles. To unlock the next level through gameplay, the player must guess the right word or words that the game expects them to make from the tiles. They confirm their guess by drawing a line or auto-highlighting across the tops of each tile in the correct order. They can only draw in left, right, up or down directions. They can't draw diagonal lines.
Fillwords rewards the player with stars and coins. The player wins stars for levels and coins at the end of each level. They receive daily bonus coins. After so many levels, they also unlock gifts that provide additional coins. The player uses their money to buy hints via a green-and-white button marked with a yellow light bulb. They can also earn additional hints by watching ad videos.