Onto is a word that shows movement toward and then upon a surface or position. When you climb onto a chair, you move from the floor up and then rest on top of it. When you jump onto a trampoline, you land on its surface. When you copy notes onto a clean sheet of paper, you transfer them to that new page.

If you pour juice onto the table instead of into your glass, you've made a mess because the liquid ended up on top of the table's surface. A cat leaping onto a windowsill moves through the air and lands there.

Sometimes people confuse onto with “on to” (two words). Use onto when describing physical movement to a surface. Use “on to” when “on” belongs with the verb: “Let's move on to the next chapter” or “Hold on to your hat.” The distinction matters for clear writing.