Along; in accordance with — a connective expression meaning 'following' or 'parallel to' something, used for physical alignment or following a plan/instruction.
川に沿って歩くと駅に出る。
If you walk along the river you'll reach the station.
お客様の要望に沿って提案書を作成しました。
I prepared the proposal according to the client's requests.
図面に沿って正確に部品を組み立ててください。
Assemble the parts accurately following the drawings.