Learn Dutch: Het afval in de bak deponeren. - Deposit the waste in the bin.

Using the full verb (the infinitive) is a common way to give impersonal commands in Dutch. You will see this mostly on public signs, packaging, and written instructions. It sounds like a general rule for everyone rather than a direct order given just to you.

If deponeren is the command, why is it placed at the very end of the sentence?

When you use an infinitive as a command, it behaves like infinitives normally do in Dutch: it gets pushed to the very end of the clause. Instead of starting with the verb, you state what and where first (Het afval in de bak), and finish with the action (deponeren).

Is deponeren the normal word to use when talking about throwing things away?

Not in everyday speech. If you are talking to a friend, you would usually use a verb like weggooien (to throw away) or doen (to do/put). Deponeren means to deposit and is quite formal, which is why it fits perfectly on an official public sign.

Why is it het afval instead of de afval?

Afval (waste or trash) is a neuter noun in Dutch, so it always takes the article het. Since it is an uncountable mass noun, you will not see it in a plural form, but you still need to remember its specific gender for things like adjectives and pointing words (like dit afval).