Hello goofygrape,

For Alpha, you need to create .png or .psd (prefered). The simplest way if you get a tileable texture is to load it in your texture pallet, select it and on the bottom of the pallet, press the "make alpha" button. It will appear in the alpha section on left of the viewport. Click on it and export.

You can save it in your zbrush alpha folder or if you prefer to access it directly, under startup/Alpha folder. It will appears in your Lightbox alpha folder to load it rapidly. Generally, I do it directly in photoshop to adjust every parameter and save it as .psd.

If you want to create a brush, open your brush pallet. You can keep the standard brush to start. Load your alpha in the alpha box.Between "standard and alpha, you can select the way to apply you brush. Dots will repeat with a defined interval, drag rect will draw on the selected point (you can extend and rotate your alpha by dragging the mouse), etc...

Then, open your stroke pallet to modify the behavior of your brush. Once done, load a sphere, turn it to polymesh, subdivide and test your brush. Adjust settings in your brush and stroke pallet.

When you are satisfied with your setting, save it with the "save as" in the top of your brush pallet. Once again, save in your zbrush/ brushes or Startup/Brush folder. Remember that brushes can manage geometry details but also colors.

For tools, it's modeling...So many tools in Zbrush, hard to know how to start.... To create a rock, you can start with a poly sphere, deform it in low poly definition to get the rough shape, Zremesh with a low value to get a simple object, UVmap it, subdivide again and apply your custom brush to get effect and colors...

Those are the basics, the best is to browse for specific topic in Zbrush tutorials on their website or on Youtube.

Hope it replies,

Best regards,