Could you please explain the differences between these two verbs?

develop a skill
foster a skill

Sometimes no difference is intended.
But 'foster' suggests more care, more deliberate efforts to make the skill 'grow'.
With 'develop', it can sometimes be by accident, without really trying.

Students: We have free audio pronunciation exercises.
Thanks, Clive. So if, for instance, I wanted to describe what the school did to me, should I say "Schools helped me to gradually develop my writing skill" or "Schools helped me to gradually foster my writing skill".
I guess for this "foster" is better : By writing daily events I've fostered my writing skills.
The school did not help you to foster your writing skill, the school fostered it.