The speaker was not clear and I couldn't make ___ what he meant.

Make out (Phrasal verb)
Meaning: manage with some difficulty to see or hear someone or something.
Bangla Meaning: বুঝতে পারা।
Example Sentence: In the dim light, it was difficult to make out the illustration.
Similar: see, discern, distinguish, perceive, pick out, detect, notice.

Here, make out is the appropriate phrasal verb to make sense of the following sentence.
The speaker was not clear and I couldn't make out what he meant.
অর্থ: বক্তার ভাষা স্পষ্ট ছিল না এবং তিনি কী বোঝাতে চেয়েছেন আমি তা বুঝতে পারি নি। 

Source: Oxford Dictionary