Microtubules are usually discussed with microfilaments. Although they are both proteins that help define cell structure and movement, they are very different molecules. While microfilaments are thin, microtubules are thick, strong spirals of thousands of subunits. Those subunits are made of the protein called tubulin. And yes, they got their name because they look like a tube.
Elements of the Cytoskeleton

All of the microfilaments and microtubules combine to form the cytoskeleton of the cell. The cytoskeleton is different from cytoplasm (cytosol). The cytoskeleton provides structure. Cytoplasm is just a fluid. The cytoskeleton connects to every organelle and every part of the cell membrane. Think about an amoeba. All of the pieces work together so that the foot might reach out towards the food. Then lysosomes and peroxisomes are sent to begin digestion. The movement of the cell membrane, organelles, and cytoplasm is all related to the tubules and filaments.

Moving Chromosomes

Microtubules have many more uses than just cell structure. They are also very important in cell division. They connect to chromosomes, help them with their first split, and then move to each new daughter cell. They are a part of a small pair of organelles called centrioles that have the specific purpose to help a cell divide. Once the cell has finished dividing, the microtubules are put to work in other places.
Moving Organisms

Beyond the role they play in internal cell movement, microtubules also work together to form larger structures that work on the outside of the cells. They can combine in very specific arrangements to form cilia and flagella. Cilia are little hairs you might see on the outside of a paramecium or other protists. They flap back and forth to help the cell move. Flagella are long, thick tails. They whip around and sometimes twirl, pushing the cell along.