How are the individual English phonemes pronounced to make a whole word? How are they joined in speech to give correct pronunciation?
Sadly there is not one answer. English as a language evolved over a succession of invasions (first the Romans, then the Vikings, then the French) and a lot of trade and migration so that these days there are the remnants of several languages and language families stitched together. Add to that that spelling became defined during a period where pronunciation shifted significantly means that the English language as written and the language as spoken differ significantly.
English is full of heteronyms, where a single word as written (say, bow) might have multiple pronunciations (one with a o and one with a a) and a whole bunch of meanings (weapon, decoration, part of a ship and gesture of respect)
And also homophones, that might be written differently (and carry different meaning based on the written word) but pronounced in exactly the same way. For example rapped and wrapped. Rapped can mean several things (to knock with your knuckles or sing in the the rap style) and wrapped is pronounced in pretty much the same way but can mean even more things (to be covered by something or to have finished, mostly projects)
And then I'm just talking about simple, middle-of-the-road English without any significant dialect. As it becomes a world language something written by someone from India might be pronounced differently than something written by a Scot, just because the writers speak very different dialects.
How are they joined in speech to give correct pronunciation?
Nobody knows, everyone just tries their best.