I am a very beginner with QGIS. I would like to know how to align two shapefiles in QGIS. The image below shows the mismatch:
I'm no expert, But there could also be a projection problem. Do both files have the same projection?
If the files don't have the same projection GIS programs may try and project display them on the fly resulting in slight miss alignment of the files.
The black outlined polygon shapefile extends into the ocean (presumably, could be lake though) whereas the purple polygon shapefile extends to the shoreline. The difference in boundary is common with administrative boundaries.
There are some areas in the north (assuming north is up) that the boundaries do not align which should be similar. This would be caused by the digitization of the shoreline. you can imagine that precision, accuracy, etc all play a role in how accurate a shapefile is created and can thus cause some small level of difference in the boundary match.
See the image below - where the peach coloured line is the administrative boundary and the blue line is the shoreline boundary respectively.
If you require that they both have the same boundary line I would suggest completing a spatial join or copying the table features into the geometry.