Before I whisk you away to the grand world of Power Auras, let me give you a little description straight from the Curse Add-On Page (Power Auras Classic - Addons - Curse).
This addon was created to provide visual cues (auras) when you gain buffs, debuffs and many more. Very useful for shorts buffs or debuffs, it allows you to draw in the center of the screen, or around your character, very customizable visual effects, rather than having to look at or mouseover buff/debuff icons/actionbars.
Initially created to give visual cues for short duration procs like "clear casting" or some boost trinket you activate, many more aura triggers have been added since.
It now works with debuffs (whatever their name), debuff types (like Magic or Curse), combo points, harmful area spells, weapon enchants, Health, Mana, Rage or Energy thresholds, action cooldowns, aggro, pvp status and stance or shapeshift form.
Essentially, PowerAuras is a way to keep track of particular buffs or debuffs or events you may otherwise have a hard time seeing or realizing they're going on. With PA; any buff, debuff, proc, missing buff, health or mana threshold, AoE you're standing in, cooldown, combo points, rage/energy/runic power, aggro or spell being cast on you can be tracked and made visible anywhere on your screen through an icon that you pick and customize. Neat huh? Now if you're sufficiently intrigued, I'll walk you through some of the basic setups of PowerAuras based on my priest's settings.
To start out and open the PA configuration window, type /powa, then click on "New".
A new window will pop up that might seem a little overwhelming at first. Now, everything depends on what kind of effect you want to set up. Let's start with setting up a proc. This is useful for trinket procs, spell procs such as clearcasting, surge of light, weapon procs and anything similar you wish to track. Any proc you get will show up as a buff, so shift your view about halfway down the new window and enter "Buff" as "Activation by".
If this proc/buff you're trying to track is a stackable buff, you may want to choose to add the minimum amount of stacks you want to have before you get the notification. IE, I have a notification that tells me when I have three stacks of serendipity up so I know at a glance when my PoH is going to be fast, and for that I enter "=3" in the stacks field. If I wanted it to show up at 2 stacks already, I would enter ">1". If your buff or proc isn't stackable, just leave the field blank.
In the field with the three question marks, enter the name of your buff. For example, "Surge of Light". If it's a trinket proc, make sure you know the name of the buff the trinket proc triggers.
If you want to track when a buff falls off - for instance, if you have a self-buff like Fel Armor or Inner Fire that you tend to forget to re-cast and you want to receive a visible notification for when it falls off, make sure to check "Show when not active". You can also choose to have the notification only pop up when in combat or in a raid.
Now we have the basic settings, it's time to adjust the look of our buff. You can of course add your own textures to PowerAuras, but when you're just starting out, it may be best to stick to the WoW textures of even just the buff/debuff graphic in question.
Make sure to keep "Glow" checked - else it's gonna be pretty ugly - and to have a bigger window of options, also check "WoW Textures".
Pick one you like with the slider, adjust its opacity, symmetry and deformation to suit your needs and pick a color you like by clicking on the little swatch below the texture preview. When you have all that set, you can adjust size and position with the sliders right below. To get a preview of your buff, click on "Test" in the main PA window.
This is what the effect I just added looks like in action:
Well, not the Val'anyr proc, just the orange bits.
Next, let's set up a debuff.
You go through the same process of picking a suitable effect/animation for your purpose, set its name, and the only difference there is is in the "activation by" field. Depending on what it is (either a debuff on you, like Mortal Strike or an AoE debuff like Rain of Fire) you pick "Debuff" or "AoE Debuff". If you want to get alerted whenever you have a certain type of debuff on you (Magic, Disease, Curse or Poison), select "Debuff Type" and enter the type in the name field afterward. Here's an example:
If you have a spell or ability with a cooldown you wish to track whenever it's available, select "Action useable". Here some examples in action:
And to finish, some of my custom buff/debuff examples. What you find useful greatly varies by class and role, so get creative!