"La lámpara está sobre mi escritorio."
Translation:The lamp is on top of my desk.
"Sobre" technically can mean "above" but usually means "on (top of)". To avoid confusion Spanish speakers would use "(por) encima de" or "arriba de".
The first (conjugations of ser) is always used for permanent things, like descriptions of someone's character, physical appearance, occupation, or nationality - generally things that are pretty permanent or "inherent" - whereas the second, está, which is a conjugation of estar, is location or current feelings (happiness, sadness, contenta, triste...), so things that tend to be more temporary. I'm sure we'll learn about it more as we get to it.
So, "mi mamá es alta" (my mom is tall) uses ser because that's a physical description (and she's going to stay tall for the most part), and "estoy contento" (I'm happy, I end it content- an o because I am a guy) because I'm happy right now (and when I have to do the dishes I might not be so happy...). I think, but I'm not sure, that if you said "soy contenta" you'd be implying that you were generally happy, or content., instead of just happy at the time. I do know that if I said "estoy aburrido," I'd mean that "I'm bored [right now]" whereas "soy aburrido" would imply that I am a boring person!
In the case of this sentence, it's describing the lamp's location, so you'd use estar.
You seem to have an unnecessary 'the' in your sentence. "On the top of" is an awkward sentence fragment
Es (ser) and está (estar) may be translated as the same (to be), but they mean different things and can't be used in the same situations. "Está" here expresses a location, and that always goes with "estar".
Está is used for temporal expressions of "to be". There's a later lesson on the difference.
DL suggested stays as meaning to esta. But "the lamp stays on top of my desk" was marked wrong. Correct translation given was "the lamo is on top of my desk"