Unstressed syllables are pronounced shorter and softer /ə/.
The most common sound in English is /ə/.
Example: First, you say these sentences.
1 – 2 – 3 – 4
1 and 2 and 3 and 4
1 and a 2 and a 3 and a 4
1 and then a 2 and then a 3 and then a 4
Now listen to how a native speaker says them using reduced /ə/.
Repeat these sentences until they are all the same length and rhythm.
Important words, the numbers 1 2 3 4, are stressed.
Unimportant words are unstressed, reduced, pronounced /ə/.
and = /ən/
a = /ə/
then = /ðən/
Reduction is when we don’t stress a vowel; we reduce it and say /ə/.