شيئاً فشيئاً means something like slowly/ little by little/ gradually e.g: لغتي العربيه تتحسّن شيئاً فشيئأ my Arabic is getting better ( improving) gradually أقترب من هدفي شيئاً فشيئأ I'm slowly getting closer to my goal hope I could help you :)

it means bit by bit "slowly"