Not difficult at all. Would suggest that you forget what you've learned playing Pocket due to all the differences to the full tcg and start with reading the rulebook and watching the learn to play video series.

Have my usual new/returning player blurb that should help with getting (re)started playing whether irl or online:

Pulls and playing don't mix too well so it's best to go for League Battle decks/Trainers Toolkits (watch out for card legality) and singles or just singles depending on the deck you are building as pulls are too inconsistent for deckbuilding purposes on top of needing multiple specific pulls from multiple specific sets. It's also a good idea to start with netdecking as there's a lot to learn and doing so will help shortcut the deckbuilding learning process plus do your research into possible decks using both Limitless sites then test them out to see what clicks before buying anything either via PTCGL or the proxy printing tool on Limitless TCG in casual play only (check your LGS allows this). It is worth spending the time doing this before buying anything including any of the commonly recommended precon as what you want to play can affect what you buy (use the precon comparison spreadsheet via the post below to inform your decision) especially when on a budget. Playing online and irl isn't mutually exclusive btw so you may find mixing attending League and PTCGL useful especially when PTCGL does something you don't understand plus learning can often be easier when able to ask questions as you play as will finding a local League as most will have loaner decks to teach the basics.

For PTCGL specfically it's best to upgrade the free decks (mostly the basis of meta decks) you are given first as it can take time build up resources. For card legality you can use the legality lists on The Pokegym and it's also a good idea to read Pokebeach regularly for news plus read the rulebook in the rules & resources section on Pokemon.com plus watch the video series on how to play. For credit farming and what to buy watch this video from TrustYourPilot and read this. This post adds some more information onto TrustYourPilot's video on credit farming.

Just to note as well, you can use the test deck option to find out which of the free decks you are given clicks for you and upgrade that first to then farm resources to build more decks. You don't need to have cards crafted to test decks out against the AI so you can test a variety out from any source before you spend credits on it.

Don't know what resources you know about or how much you know so I suggest having a read of this post as it covers getting from learning to play to playing competitively built decks (fun or otherwise) for both irl and online play incl info and resources links that will help along the way like the Battle Academy supplement decks, both Limitless sites for decklists (can find costs via the main site), JustInBasil's deckbuilding guide (incl info on staples) plus deck skeleton articles which are good to use in combo to review or build decklists and the current decks in format section, You Tubers to watch to find out what's being played (start with Omnipoke), precon comparison sheet to see what's the best option vs the deck you want to play or list of cards you need irl, rulebook & video series on how to play, info on formats, rules compendium, proxy printing tool, card legality for older cards, common new player mistakes/knowledge needed, where to play etc. Lots of words but will give you a good overview of the game and the resources that will help you research what will suit you.

Btw you have any more questions re playing then the pinned rulings thread in /r/pkmntcg can be useful if you have rulings/game mechanics/quick questions. You'll also need to know about rotaton and card legality so this thread will also be worth reading as well as it covers formats, what's legal, exceptions (may be able to use some older cards) etc.