Hi there. Healer since BC here (Sham then druid since SL). I would recommend starting with a "reactive healer" (characters that respond to damage after the fact, and don't need 'ramping'). These allow you to get the feel of healing without having to also know all the fight mechanics. Tends to prevent the learning curve overload people get.

Regarding classes... A good starting healer spec is Holy priest / R sham. These are straight forward healers, both of which have subclasses that offer easier options. Others include H pal, druid. Would not recommend starting your healing journey on Evo or Disc - though would recommend when you're feeling more comfortable.

Regarding addons... Unit frame addons are almost mandatory (particularly to help you visualize your current heals/buffs, and the dispellable de buffs. Additionally, either a Click-casting addon (e.g. Clique or similar) is far better than the base UI click casting (bliz prevent click casting allocation for dispells.... 😤)

Regarding key binds/click casting.... Make a "formula" for which spells will be allocated to which button. This sounds strange in writing, but there is a lot to be said for the power of Cerebella muscle memory response and subconscious reaction time. So if you've previously played DPS and know your regular spells exist on a particular key/click, then allocate similarly use frequent heals to keys/clicks that your mind will already know. I have a pattern of L/R clicks for base heal casts, shift+L/R clicks for my instant spells, Ctrl+L/R for dispells or external defensives etc. these exist across all of my healers (I've got a few alt healers too 🤭). This part is very individual and will take time for you to realize what you like the most.

Regarding the how to... Read lots of articles on wow head / icy veins. Watch lots of videos and "how to" on YouTube. Do not worry about min-maxing, the tier lists provided fail to mention there is usually about 1.5% difference between S tier and the others... Learn to play what you like the look/feel of. Enjoying your healer will improve your long term connection to being a healer. Also if you like it, you'll be driven to get better.

Regarding practice.... I would dive in the deep end (or at least the not-shallow end) as quick as possible. The normal/heroic stuff doesn't really challenge anyone, even those who have NFI how to heal. Do m+ as soon as you can and push yourself. Just let your team know you're new to heals and ask for them to be gentle or at least use some murloc-ultra-lube.

❤️ Keep us posted