So pretty much all of the major online card rooms offer play money to learn how to play the game, pokerstars, 888 & partypoker. I'm sure other reputable ones offer play money options too.
As for a client that allows for offline and online options, I don't think one exists from my knowledge. Your best bet would probably to download a poker video game, something like
governor of poker or
Poker Night at the Inventory.
So some things with the relevance as these as a learning tool to consider:
- People won't play seriously with play money as such it's not a great way to learn anything other than the very basics.
- Playing offline against bots will only again teach you the basics as often these games against bots end up being find how to exploit them do that every time.
As a side and something that I think would be a better way to learn would be to pick up some poker books, there are many great ones out there, even though it's rather old
Harrington on Hold'em is a nice starting book, especially to a basic solid ABC style of poker. Once you've finished reading some basic books, you can move onto more advanced books, Jonathan Little has several great poker books,
Essential Poker Math by Alton Hardin,
The Raiser's Edge (Old but still good), etc.
Honestly you're a blank canvas, and my biggest piece of advice to learning poker as someone who hasn't played before, is learn it the right way. Don't learn the way a lot of people do by playing first. I think a huge percentage of poker players who are winning players will tell you all of their initial bad habits from learning the game which they had to then go unlearn over the years. It's extremely hard to unlearn a bad habit and there is no better way to pick up a bad habit than to jump into something you have no idea about and end up getting lucky.
TL;DR I'd recommend picking up a few books, read them, then play some play money or low stakes cash. Really though you have an amazing opportunity, with a huge wealth of poker knowledge shared now in books for you from some of the greatest minds in Poker, use that rather than playing initially.