Correct sentence (fixed grammar and capitalization): Capillaries are the tiniest blood vessels that connect arteries and veins.
What that means: Capillaries are very, very small tubes in your body. They connect the bigger blood tubes (arteries and veins). Blood travels through capillaries to give cells oxygen and food and to take away the waste.
Easy example: Think of roads: arteries are big highways, veins are big roads back home, and capillaries are tiny little streets that reach every house (every cell).
- Capillaries are much smaller than a hair — sometimes blood cells go through one at a time.
- They bring oxygen and nutrients to your cells.
- They carry away waste like carbon dioxide.
Grammar note: Your original sentence was almost correct. Don’t use all capital letters for 'CAPILLARIES' — write 'Capillaries'. You can also say: "Capillaries are tiny blood vessels that connect arteries to veins."