Bilabial consonants are made by using both lips, labiodental consonants by using your top lip and your teeth. Some learners have problems recognizing the difference between labial and labiodental consonants. Spanish speakers, for example, have problems with /v/ and /b/.
Example
/p/ and /b/ are labial consonants, /v/ and /f/ are labiodental consonants.
In the classroom
Asking learners to distinguish between minimal pairs such as ‘ban' and ‘van' and ‘bet' and ‘vet' is one way to help them learn to recognise these sounds. Learners can make pairs themselves for other students.
Further links:
https://www.teachingenglish.org.uk/article/same-sound-different-sound
https://www.teachingenglish.org.uk/article/voiced-unvoiced-consonants-0
https://www.teachingenglish.org.uk/article/teaching-speaking-unit-3-individual-sounds