Do you play the physical card game or the TCGO? The things you're going to need to get started will be a bit different depending on which one it is. I can tell you a little bit about the online game to give you some starting pointers.
I think that either way though, you should start by playing Theme Decks, specially if you have little to no experience with the Pokemon TCG (doubly so if this were to be your first time picking up a TCG). Playing Theme Decks will allow you to familiarize yourself with the rules and some of the basics of the game. Most of the recently released Theme Decks are good, but I think that what's strongest in the current Theme meta right now is Blazing Volcano, so that's a good starting point. Online, after completing the tutorial and playing a few VS matches with one of the default Theme Decks you should have around 500 Tokens, which is how many you need to buy a Theme Deck from the store.
Initially, I wouldn't recommend that you spend any Tokens on buying booster packs. The packs that you can buy with Tokens are all tradelocked (meaning that those packs and the cards contained in them cannot be traded), so you won't be able to trade anything of value you pull. I'm mostly thinking here that, besides needing luck to pull useful cards, even if you do pull something of value you won't be able to trade them for a different card that you need.
After you buy you first Theme Deck, I think that spending Tokens on other Theme Decks is a better investment thatn buying packs. These will still be tradelocked, but there will be no luck involved; the 60 cards that come with it are guaranteed. Many times these decks, despite not being competitive against custom (Standard and Expanded) decks, they contain many "staple" cards that are typically used on any deck. For example, if you needed Cynthias for a deck (you probably will if you decide to play Standard later), the deck Mach Strike contains 2 of them (along with several other goodies). Sometimes you can also make budget decks that are still viable by taking most of the pieces out of Theme Decks that you bought. Continuing the Mach Strike example, if you decided to play a Standard Garchomp deck, just by buying Mach Strike from the store twice (which would cost you 1000 Tokens) you already have 90% of the deck completed.
If you're playing IRL, I still think that staring with a Theme Deck would be a good idea, but you're gonna need a buddy to play with that either has mercy on you, or also plays a Theme Deck against you so that the field is even.
As fun as it is to open Booster Packs, buying singles is more cost efficient. After you get used to playing the game and decide to make a Standard or Expanded decks, when you've decided on what deck you want to play you would need to find a good place to buy singles from.
If you do play IRL though, I'd recommend that you play in the TCGO to practice first. By the time you start buying singles you want to have a good idea of what you need already so that you don't waste money buying random cards you can't use.
If there's anything else I can do for you, let me know.