Well play the game first, if you don't love it then you won't want to spend the time required to get really good at it. You might wanna look into Livesplit which is a widely used timer in speedrunning. TL DR: Speedrunning a game requires A LOT of grinding and practicing and it takes time, but I think when you finally land all the strats first try the feeling is really good. I copied the strats from them and just tried to mimic them as well as possible, you could try that too. But if you want to learn that's really cool, I started to run Half-Life 2 just recently after watching a ton of HL2 runs. And generally I think that speedruns are by definition not that easy since you are trying to beat them as fast as possible. Some strats are hard and involve a bit of RNG and there are long cutscenes.
Episode 2 could be a nice first game to run since it's not that long (WR being 43:35). Most important strat is ABH which might take a while to master but it's very rewarding and fun once you actually can move really fast. I assume you're talking about Half-Life 2: Episode 2 since it was just ran by Gocnak.
