Learn Turkish: Resim duvarda. - The picture is on the wall.

The locative suffix (which means in, on, or at) changes to match the vowels in the word it attaches to. Because the last vowel in duvar (wall) is an 'a', which is a back vowel, we use -da. If the word ended with a front vowel like 'e' or 'i', we would use -de.

How do we know duvarda means "on the wall" and not "in the wall"?

The suffix -da covers "in", "on", and "at". You have to rely on common sense and context to translate it into English. Since a picture hangs on the surface of a wall, "on" is the logical choice here.

Where is the word for "is" in this sentence?

There isn't one! In Turkish, the "to be" verb (am/is/are) for the third person ("he/she/it") is often completely left out. Just putting the subject (resim) and the location (duvarda) next to each other is enough to say "The picture is on the wall."

Why isn't there a word for "the" before resim?

Turkish does not have a specific word for "the". When a noun is the subject of a sentence like this, it is usually understood as specific ("the picture") rather than general ("a picture") depending on the context.