I have a pencil in (meaning on) my desk. Tengo un lapiz en mi escritorio/pupitre/carpeta (alternatives for 'desk') I have a pencil in[side] my desk Tengo un lapiz dentro de mi escritorio.
It is not a pencil.
"Un lápiz de colores" translates to "a colored pencil" in English.
Tengo means 'i have' if you had the phrase 'Tengo un problema' that would mean in english, 'i have a problem'
"Necesito un lápiz" means "I need a pencil" in Spanish.
I have a house
I have a brother.
"Mijo yo tengo un novio" translates to "Son, I have a boyfriend" in English.
That you are tired!!
It means "have a love", and can be stated as a question.
I have a game tomorrow.
I have a big car.