In what ways does a language lab help the learners learn the language?

It gives them the opportunity to hear native speakers speaking the
texts and exercises related to the language course and practice
speaking themselves, also allowing them to compare their pronunciation
with that of the native speakers.
This helps them learn to hear and pronounce the sounds in the foreign
language that are different from those in their own language and thus
improve their accent.
OF course, one can practice speaking without a language lab, but then
one does not have this immediate control and gets in the habit of
making typical errors that are then very difficult to get rid of:  for
example, Germans saying:  "ve vere" instead of "we were,"  or
Americans saying:  "isch" in German instead of the correct gutteral ch
of "ich".