How to use 'sobre' and 'en'?

How to use 'sobre' and 'en'?
 

La lámpara está sobre la mesa.
Los hombres están en la mesa.
El hombre está sobre la mesa.
La mujer está sobre el automóvil.
La mujer está en el automóvil.

Why sometimes we use sobre sometimes we use en?What is the difference between la and el?I am really confused@@

When meaning 'on', you can use 'en' or 'sobre' - they mean the same. But 'en' can also mean 'in'

In Spanish, nouns have gender - they are either masculine or feminine. Masculine nouns need el, feminine nouns need la

El hombre, los hombres
La mujer, las mujeres

You can guess those two, but you have to learn the gender with each noun. Normally there is no obvious reason why a noun has a particular gender: la salchicha, the sausage.