You can adjust the symbol for the points in a vector layer:
Click on the relevant layer in the Layers Panel
Click on the Style tab on the left side of the Layer Properties window
In the top-most bar, choose Single Symbol
You can adjust size, colour and transparency and choose another symbol from the Library
Click on OK
Points, lines and polygons can be shown in different categories in the map image. This is especially useful when an attribute can only have a limited number of values, such as motorways, types of livestock farms, etc.
Click on the relevant layer in the Layers Panel
On the left side of the Layer Properties window, click on the Style tab
Choose Categorized in the top-most bar
At Column, choose the attribute of which you wish the values to be displayed in the map image
Choose Classify
You can adjust colour and colour ramp
By clicking on the symbol in the window, you can adjust this too
Click on OK
You can have Qgis classify the attribute values of points, lines and polygons of a vector layer and have these displayed in the map image in different colours.
On the left side of the Layer Properties window, click on the Style tab
Choose Graduated in the top-most bar
Choose Colour at Method
Choose a Colour Ramp or click on Edit to make one yourself
Choose a classification method and click on Classify
Click on OK
By this you can show the size of a particular value within a vector layer. To this end, Qgis creates a number (indicated by you) of classes. These can be seen in the map image as symbols (such as circles, stars, etc.) of different sizes.
There are several ways for the different types of data:
Points
A file containing point data can be given different symbols and also symbols of different sizes.
Polygons and diagrams
Polygons and centroids
In a vector layer consisting of polygons with statistical data per area in them (e.g. per municipality), you can also have these data displayed in graduated symbols. To this end, you will first need to make a layer containing the centroids:
Style your centroids as you would style a layer of points: