The letter R (ere) represents two different sounds, [r] and [rr]. This contrast is a distinctive opposition, so it’s important to be able to pronounce and understand it.
There are no sounds [r] and [rr] in English, the English [r] has nothing in common with the Spanish variants. The sound [r] is tap, it is articulated in the same place as the sound [l]. The tongue slightly touches the hard palate.
The sound [r] cannot be at the beginning of the word, though it appears in all the rest positions:
caro, parar, prado
[Rr] it is articulated in the same place, though it is trill, more “growling” than in English. You must "roll" it.
At the beginning of the word, or after the letters -n-, -s-, the letter r is always pronounced as [rr]:
Roma [RRoma]
Rita [RRita]
Enrique [Enrrike]
The sound [s] before [rr] is not pronounced:
Israel [Irrael]
las rosas [larrosas]
The trilling [rr] between vowels is represented by double rr:
perro, carro
Use rr only between two vowels.