I started making a vector layer from raster data but I see slivers (gap area) between my parks and roads layer. How can I overcome this problem? I planned to make a map with scale 1:5000.
The title of your question was misleading. Your issue is more probably about snapping, which is one of the several tools used for digitizing features.
Simply, enable snapping mode from
Settings >> Snapping Options....
Then, try to use the
Node Tool and the
Move Feature(s) tools from the main QGIS window (they are activated once you have set the layer in editing mode):
These are only general rules and are necessary for starting the digitizing operation: if you need a more specific answer, please edit the question for adding more information or ask a new separate question if you encounter any problem after having applied these suggestions.