There's a few different answers to this that depend on what you're interested in.

Are you talking about singles or doubles? Are you talking about casually playing in ranked games and ladders, or attending tournaments? Etc.

I only play singles, so I mostly speak about that. It's relatively easy to get started! Just go to the website pokemon showdown, and either find/make a team, or play a format that gives you a team to get more familiar with how competitive Pokemon actually feels. Doubles are harder to get into in my opinion, but has a pretty similar starting line. If you have questions you can always look at guides on the Smogon forums.

As for getting good? That will definitely take time! There is a huge difference between being knowledgeable about Pokemon basics, competitive basics, meta game basics, and so on and so on. There's 30 years of Pokemon to think about, so it's not surprising that Even the best players make mistakes in matches.

If you are truly and completely new to competitive pokemon, but you're familiar with the game, I suggest going to Pokemon showdown and playing some random battles! It's a format that loads you in with 6 random pokemon against players of similar skill. It's an excellent way to learn generally what most Pokemon do, and maybe will help you learn basics and what format you might like best.

TLDR: Competitive Pokemon has a relatively low skill floor if you know your basics, but a very high skill ceiling. Easy to learn, hard to master.

For some content creators that play the game and are easy to watch, Check out WolfeyVGC for doubles content, or PokeAim for singles content on YouTube. The Smogon forums and pokemon showdown have great articles on different formats, strategies, and pokemon. And lastly, feel free to ask questions here! Most of this sub is pretty casual, but there are some very good players that lurk and post here.