Extent is a noun. It roughly means 'limit'. For example: The extent of his knowledge on medicine is limited, as he isn't a doctor. Expand is a verb. It roughly means 'to grow'. For example: My uncle wants to start two new stores in London to expand his business. Hope this helps. Check out my English lessons, if you're looking for coaching. Good luck

In case you are asking about extend and expand. Sparkymark has answered really well. I'll just extend his answer a little bit. You can extend a line to make it longer. (lengthen) Your teacher may extend class duration. (prolong) You can expand the volume of a container. (volumetric increase) You can expand your living room. You can expand your knowledge of the English language by asking stimulating questions like this.

Unless you are thinking about extend and expand - Extend is to lengthen - I extended my vacation for another week. Expand - to make bigger