the zh or j sound may come from combination. Such as zhe er這兒.this type of words contain the r sound but also contain the zh sound. It’s like in English, when you say care, it contain the r sound but also contain k and a sound.
In Chinese the pure r sound is very similar to English. Only the tone is different. (Chinese goes up, second tone二聲，in English goes down, fourth tone四聲)