Not every possible sound has been given its own simple symbol. In these cases, we must modify the closest symbol with diacritics. For example, we can create a symbol for the voiceless alveolar nasal stop by placing the voiceless diacritic (a circle) underneath the symbol for a the voiced alveolar nasal stop, [n]. We can create a symbol for the voiced bilabial approximant by placing the "lowered" or "more open" diacritic (a small T with the line pointing downward) underneath the symbol for the voiced bilabial fricative, the Greek letter beta.
It is possible to have bilabial fricatives as well as stops:
This ambiguity wasn't too problematic during the formative years of the IPA, since most of the languages that were then familiar to western linguists never contrasted the three POAs except in fricatives. English would use alveolar stops, French would use dental stops, but none of the familiar languages would use both in a way that could change the meaning of a word. But there are languages which do make such contrasts: many Australian languages contrast all four coronal POAs; many languages of India contrast at least dental, alveolar, and retroflex.
We have been calling the  sound of English a retroflex. Yetthe symbol for it appears in the IPA chart in the dental-alveolar-postalveolar mega-column. The English R-sound (the non-"bunched" version) certainly counts as an apico-postalveolar and has a legitimate claim on the symbol even without a retracted diacritic. The tongue tip is certainly more curled back for an  than for any other sound of English. But the amount the tongue is curled back isn't too impressive when compared with languages which have a whole set of true retroflexes (e.g., languages of Australia or India). In some languages, retroflexes are so extreme that the tongue tip touches the hard palate or contact is made by the underside of the tongue tip.
R-sounds in Irish English are typically more retroflex than those of western Canadian English.
Most of the languages of India have retroflex stops. As well, Indian English typically uses retroflex  and  where other dialects of English would use alveolar [t] and [d].
Mandarin Chinese has retroflex fricatives and affricates.
A voiced retroflex fricative can be the nucleus of a syllable:
 chi `eat'
The voiceless palatal fricative [ç] is used in German ich.
A palatal nasal is used in Spanish señor and French oignon.
English uses the glottal "fricative" [h] -- in reality, a breathy voiceless articulation of the neighbouring vowels -- as if it were just another consonant.
Many languages also use the glottal stop  as if it were just
another consonant. English doesn't, except in a few odd corners
such as the interjection uh-uh. In many dialects of
English, it is also common for an voiceless stop in the coda of a
syllable to have glottal stop begun just before and overlapping
with the closure phase of the higher stop.