With texture painting on Blender, there are a few steps you need to take before pulling out that pain brush and painting your model.
Also, the complexity of texture painting will also depend on the complexity of your model. So in this mini guide I opt to demonstrate the steps to texture painting using a very basic model such as a cube.
The assumption here is that if you are a decent to good modeller, then you likely know how to texture paint. In essence, this is a starting guide and using a basic model will likely get the message across which you can then replicate on more complex shapes and geometry.
So What Is Texture Painting In Blender?
As the name suggests, this is a built-in paint feature designed so that you can physically paint over your UV textures which then transposes onto your model.

Of course there is an other option where you can download your UV texture and edit that externally using photo editing tools like Photoshop or Gimp and then re-upload.
However, in this example we’ll be doing the drawing / editing direct on the model using Blender’s texture paint tool!
Let’s take a look at the steps we shall be covering
So let’s getting started with the step-by-step guide… remember we’ll be using a simple cube for demonstration purposes.
Step 1: UV Unwrapping Your Blender Model
Load up Blender and conveniently the default cube shows up.
Go into ‘Edit Mode’ by left clicking the cube and then choosing ‘Edit Mode’ at the top menu.

In the newer version of Blender (2.92.0) the cube will already be highlighted in orange. If not highlighted in orange, simply hit the ‘A’ key on the keyboard to highlight it.

Now we want to UV unwrap the model, which is essentially the process of turning your 3D model and flattening it into 2D sections.
To do this, while in ‘Edit Mode’ (and model highlighted in orange), simply hit ‘U’ on your keyboard and then click ‘Smart UV Project’ from the menu.

Step 2: Accessing Blender’s Texture Paint Panel
At this point it would appear nothing happened, but you will now need to click the ‘Texture Paint’ tab on the top menu to see the texture paint panel AND your model in flat pack!

Step 3: How To Add A Base Color (a little like a primer coat before painting)
Notice above how your model has turned purple?
That means it has no texture to paint on. So at it stands we cannot paint anything on our model until we add a base color.
To do this, click on the ‘texture draw’ tab, then the ‘+’ button and finally select ‘Base Color’ from the drop down list!

You’ve finally added a base color and your model should have turned grey!
Step 4: Choosing Different Brushes & Paint Types
I won’t be going into detail explaining the features that come with each type of brush as I think with a little testing it will be self explanatory what they do.
So instead, what we are going to do is select a color from the color wheel (in this case blue) and then move our cursor (which is now a circle) over our model and start painting it but left clicking the mouse button and holding it down.

Note: The cursor circle (aka brush stroke diameter) can be increased or decreased in size using ‘[ or ]’ keys on your keyboard.
Step 5: Seeing Your Paint On UV Unwrap
One thing your might notice is that while painting your model, you will not see the paint show up on your UV unwrap.
That’s because you need to change one setting and everything is sorted.
Simply click the arrow pointing downwards and select ‘Material Base Color’ from the drop down menu.

Note: Now while you continuing drawing on your model, you will see your UV unwrap update in real time
You are done!