It’s definitely one of those things that you kinda just have to dive in on knowing the basics (grind out gold & xp, push up the lanes, destroy the enemies buildings and finally their base) and then you’ll slowly start to pick up stuff as it goes.
I’d say it didn’t take me too long to have a rough understanding of what was going on. When I was first watching TI, I would have the wiki open and if a hero seemed particularly interesting or important I would read into their skills.
Watching in-game can also be a good way to do that, as you can click on an individual hero and mouse over their spells one-by-one, as well as scroll the view out to a wider perspective that can make things a little easier to follow at first.
As I mentioned earlier, I did make a video specifically about coming to Dota as a viewer, but it’s two years out of date now. You might still find it useful, but the general gist of it is along these lines:
- Don’t worry too much about specifics at first.
- Focus on the positioning and movement of heroes.
- Look at objectives for an idea of who is ahead - towers and barracks are gone forever when destroyed, so they’re the clearest indicator of who’s ahead in the game.
After that, you’ll slowly start to fill in the specifics over time. Initially you might not realise quite why people are getting so excited about a certain thing, but some stuff will be obvious (such as an Enigma catching the whole enemy team in his Black Hole ultimate). Other stuff you’ll start to recognise happening repeatedly across multiple games.
As well as the newcomer stream (which is going to have helpful overlays on it), they’ve generally improved with mid-game replays of big events where they’ll slow things down and explain what happened - even for an experienced viewer, things go fast sometimes! Yesterday there was a big Lich ult (he has a ball that keeps bouncing between enemies if they’re close together and deals a ton of damage) that they broke down after the fight ended.
Also feel free to ask as many questions as you want! There’s no harm in being curious, and there will always be people willing to explain things to anyone who is interested in learning more.