For the most part the various options in the Tools Tool Options Palette are similar. One can select the Brush Tip (Shape) or use either the default tips of Circle or Square. The Brush Size can be made small or large depending upon the size of the area one wants to work with. (There will be times when one wants a fairly small size to work in detailed areas.)
A key set of options are Hardness, Step, and Opacity. One can also vary the Density, Thickness, and Rotation which are often used for certain effects and to set the brush shape to an area for detailed work.
For detailed information on the Brush Tips and Options the Help section is important to review including the topics on Retouching Images and Description of the Retouch Brushes.
Again, learning how these various options and values affect the appearance of the area painted will enhance one's ability to enhance and fix photographs very easily and effectively. Often an average looking photograph can be enhanced to be a brilliantly presented photograph.
Hardness and Opacity: Often using lower values than 100% for the Hardness (how sharp or fading of edges of brush tip) and Opacity (how opaque or transparent the area used will show) are important options to master. Often for best blending the Hardness value set low (around 50% or less) will perform well. Additional blending can be achieved by varying the Opacity value.
Step: The Step option determines the distance in pixels between the painted area when the brush (mouse) is held down and dragged or stoked in a continuous fashion. Often though just brief clicking of the mouse will be an important technique to master to blend areas together.
Density: The Density value determines how solid or spotty (or spraying effect) the painting will be in the coverage area.
Thickness and Rotation: The thickness value determines if the brush tip is full size (round or square) or is narrowed (lower values) and when thickness is lowered one can set its rotation often used when working next to the sides of an object that is not vertical or horizontal.
Continuous: When checked applying paint to the same area (multiple strokes) does not affect the result while unchecked allows one to build up the paint in the area (used when hardness and opacity values are lower).
Experiment with the Retouch Tools and their options. Always duplicate the photograph and work on the duplicate to preserve the original photo. Also, when experimenting, duplicate the bottom layer to preserve the original and experiment on the duplicated layer. Then when wanting to experiment further, or remove the trial and start again, just duplicate the bottom layer. Working on layers and turning off lower layers is an effective way to not only learn how to use tools but to have fun.