Across (पार/आर-पार - Open Area): Used for crossing open areas, surfaces, or lines (e.g., across the river, across the road, across the field).
Example: He walked across the road. (वह सड़क पार कर गया)
Through (के माध्यम से/अंदर से - Enclosed Space): Used for moving within a 3D or enclosed space, or something having depth (e.g., through the forest, through the tunnel, through the crowd).
Example: The train went through the tunnel. (ट्रेन सुरंग के अंदर से गुजरी)
Along (के साथ-साथ/किनारे - Following a Line): Used for moving parallel to a long, narrow path or object (e.g., along the beach, along the path, along the wall).
Example: We walked along the river bank. (हम नदी के किनारे-किनारे चले)