You can’t plug a shader (green output) into the color input (yellow input) of another shader. The shader represents a calculation that the render engine has to do when a ray hits the object.
You can mix multiple shaders together using the mix shader node to produce a more complex result, but for most things it’s easier to just adjust the settings for the principled shader. The principled shader is a complex shader that can be used to produce the results you need for most types of materials.
You can use cycle’s nodes to composite textures together the same way photoshop does it (including a lot of the blending options, masks, and opacity).
I explained how this works in this post:
I recommend reading that to get a better feel for how textures are composited in cycles.