Learn German: Ich kaufe heute viel ein. - I am shopping a lot today.

This sentence uses the separable verb einkaufen (to shop). In German main clauses, the prefix (in this case, ein) separates from the main verb (kaufen) and is pushed to the very end of the sentence. The conjugated part (kaufe) stays in the normal second position.

What is the difference between kaufen and einkaufen?

kaufen means to buy and is usually used when you mention the specific item you are buying, like a book or a car. einkaufen means to shop or to go grocery shopping as an activity, which is why we don't need to name exactly what we are buying here.

Why isn't the word for today (heute) at the end of the sentence like it is in English?

In German, time words like heute usually come very early in the sentence, right after the conjugated verb. Furthermore, because this sentence uses a separable verb, the prefix ein claims the absolute final spot, blocking anything else from going there.

The translation says I am shopping, but there is no word for am in the German sentence. Why?

German does not have a continuous form like the English -ing tense. The simple present tense ich kaufe ein translates to both I shop and I am shopping. You just use the normal present tense for actions happening right now.