"Yo quiero comprar una camisa."
Translation:I want to buy a shirt.
Because 'comprar' means 'to buy'. To be boring, it's an infinitive verb... and in English, infinitive verbs are expressed as 'to...' plus the verb base. E.g., 'to sleep', 'to buy'. Peeps would never say "I want buy a shirt." Similarly, they'd never say "I want to to buy a shirt."
I can hear now, i changed my ear phones, they were the problem. Duolingo is realy 2 languages for me because I am french and have to think in english so I learn 2 languages at the same time. I'm not bad in english but I have to think. It's a lot of fun. Lots of words are close to french and that helps.
These Rs you don't need to roll, only lilt them (have your toungue almost flap against your pallete like your about to pronounce the letter L).
Spanish has two types of Rs, the rolling ones and the lilted ones. If the letter appears at the start of the word (like in "rojo") or if its a double R (like in "perro"), you roll it. Otherwise it should be lilted.