The most noticeable difference among accents of English is the pronunciation of letter /r/. English pronunciation can be divided into two main accents including Rhotic accent and Non-Rhotic accent.
Rhotic English speakers do pronounce post-vocalic /r/ and final positon (before a pause) in words.
- Post-vocalic /r/ as first /fɜrst/, turn /tɜrn/,learn /lɜrn/ and party /ˈpɑːrti/.
- Final position as car /kɑːr/, better /ˈbetər/, year/jɪər/ and over/ˈoʊ•vər/
Whereas, Non-Rhotic speakers do not pronounce post-vocalic and final position in words. But only pronounce the word r is followed by a vowel as carrot /ˈkær•ət/, arrive /əˈrɑɪv/ and hearing /ˈhɪər•ɪŋ/
By the way, both accents are pronounce pre-vocalic /r/ as real /rɪəl/, ring /rɪŋ/, roof /ruːf/ and race /reɪs/
To sum up, accents which have r in post-vocalic and final position are called Rhotic accents, while accents in which r only are before vowel are called Non-Rhotic accents. Allaccents pronounce pre-vocalic /r/.