it's a bit daunting isn't it?
ok first to the mouse. do you mean the mousepad on the mac? if so, to right click hold CTRL when you click, this will give you the right click facility, as you've found out you can also make the wacom pen buttons a right click one too. i've never used the wacom mouse so i can't help you with that, i just use the pen as a mouse.
right onto photoshop, it's not like painter, painter is a 'real media' program, the layers when you get used to them are such a help, it's like painting on layers of acetate, so the layer below isn't affected by the layer above, you need to get used to using the flow & opacity in the top bar, flow is the amount of 'paint' flowing to the brush, opacity does exactly what it says, if you have say 50% opacity, your first stroke will lay down 50% density of colour, then each stroke gets 'thicker' paint until it reaches 100%. it sounds like you may be using an airbrush, do you just hold it to the wacom pad & it lays down paint? You should try other brushes.
try with the standard hard round, and adjust the flow and opacity to see what you like, you also have the smudge tool, which while it is frowned upon as it can become a crutch, it is useful in smudging the paint around a bit.
your question is massively open ended so ask your specific ones when they come up & we'll try to help. Its a steep learning curve but you will get used to it. hope this helps a bit though.