You can add feature labels to any line, point or polygon layer using the label tab in layer settings.
Labels are disabled by default. To enable labels for your layer, open the Labels tab of the Layer Settings panel and enable labels.
From within the settings you can modify the font, size and style, as well as text fill and halo color.
Labels for polygons will be rendered inside the feature, for Line features the label will follow the path of the line, and Point labels will show to the right of the point.
Advanced label placement
To configure advanced labels, use Custom style (SLD).
Note that using Custom SLD overrides standard labelling, and labels configured on the Labels tab will no longer display.