Learn Finnish: Vuori on korkeampi kuin metsä. - The mountain is higher than the forest.

The basic word for "high" or "tall" is korkea. To make it comparative ("higher"), you simply add the suffix -mpi to the basic form, giving us korkeampi.

How does the word kuin work when comparing two things in this sentence?

kuin means "than". When you use it for comparisons, the word that follows it takes the same grammatical case as the first thing being compared. Since vuori (mountain) is in the basic dictionary form (nominative), metsä (forest) is also in the nominative.

Can korkeampi also mean "taller"?

Yes. In Finnish, korkea means both "high" and "tall" when talking about things like buildings, trees, and mountains. For people, you would usually use pitkä (long/tall), but for objects and landscapes, korkeampi works for both "higher" and "taller".

I have seen comparisons that do not use the word kuin. Could we write this sentence differently?

Yes! Instead of using kuin and keeping the second word in the basic form, you can drop kuin and put the second word in the partitive case. So, korkeampi kuin metsä can also be said as metsää korkeampi. Both mean exactly the same thing and are very common to see.