Two Letters, One Sound: μπ, ντ, γκ
Greek has no single letter for the sounds b, d and hard g, so it spells each with a PAIR: μπ = b, ντ = d, γκ = g. The pair is one sound, never two. Position then decides the exact value: at the START of a word μπ/ντ/γκ are the plain sounds b / d / g (μπορώ = bo-RÓ, ντομάτα = do-MÁ-ta, γκρίζος = GRÍ-zos), while INSIDE a word they usually pick up a nasal onset - mb / nd / ng, as in English number, wonder, finger (λάμπα = LÁM-ba, κοντά = ko-NDÁ, μυρμήγκι = mir-MÍN-gi). Many speakers drop that nasal in casual speech, so plain b / d / g inside a word is also heard and always understood.
The rule
Greek has no single letter for the sounds b, d and hard g, so it spells each with a pair: μπ = b, ντ = d, γκ = g. The pair is one sound, never two. Position then decides the exact value. At the start of a word they are the plain sounds - μπορώ (bo-RÓ), ντομάτα (do-MÁ-ta), γκρίζος (GRÍ-zos). Inside a word they usually pick up a nasal onset, mb / nd / ng, as in English number, wonder, finger - λάμπα (LÁM-ba), κοντά (ko-NDÁ). Many speakers drop that nasal in casual speech, so plain b / d / g inside a word is also heard and always understood. This is the pair set the movable final -ν rule is stated in terms of, which is why it is worth fixing first.