The /ʁ/ sound is not a standard sound in English. You can think of the /ʁ/ sound in Brazilian Portuguese as being somewhat similar to a guttural or throaty /h/ sound. See notes below.
Examples:
The /ʁ/ sound is a voiced, uvular fricative or approximant sound. It's often referred to as the "guttural R" sound. This sound is commonly found in various positions within Brazilian Portuguese words, such as in "carro" (car) or "correr" (to run).
The /ʁ/ sound is produced by narrowing the space between the back of the tongue and the uvula (the soft tissue that hangs down at the back of the throat). This creates friction as the air passes through, resulting in a distinct sound.
What sets apart the guttural Brazilian Portuguese /ʁ/ sound from the smoother /h/ in English is that it's produced further back in the mouth, closer to the uvula. It involves friction or constriction of the airflow, which is what gives the /ʁ/ sound a distinct guttural quality.
NOTES
In certain regions of Brazil the letter "r" is not pronounced as the /ʁ/ sound but instead as the trilled /r/ sound. This trilled "r" sound is produced at the front of the mouth and not by friction at the back of the throat. For more on the /r/ sound, see: