I'll try not to repeat what others already said, but just a short intro:
If you are intent to create a game that needs a lot of data to be stored for later / longer usage, you definitely need some database. Yes, you can pick whatever you want for a small project - sqlite, mysql, mongo or whatever, but if you will use back-end language that works on the server side, you get the possibility to do it safer and more reliable than saving the data directly using browser's functionality and it's judgement.
I don't know a lot about RPG games, but lets imagine that I do and try to put things together to help you decide what do you actually need:
I remember myself when I was 14 years old and one of the most popular games that come to my head is Travian. I don't know if you know this game, but there you need to build your empire from scratch by building various buildings in order to get resources, then on different conditions you can create different warriours, attacking other players and grab theri resources, chatting with them, seeing atack progress, getting messages after successfull / non-successfull attack and see your progress. Your cities or towns (I don't remember well) can be expanded by building each town in some different place by using coordinates (for example 1;1, 2;1, 7;3 and so on) so therefore is a map to help players to choose which one to pick as a pray and determine the distance between your town to the target to see how long your warriours should walk to reach it.
OK, enough storry part, lets focus on the things we with my old friend did to achieve at least something quite simmlar to my description and what happened:
We definitely need somehow to create front-end to display all the game's content, so we use HTML for that of-course. Since style was important too, we used css (I don't remember if css3 was invented yet) OK, we picked javascript too for displaying warnings when user enters wrong data in the form field or does something non-desirable and also to warn the player about attacks. These days you can use js to play sounds, use frameworks to create flashing messages, even force screen reader (with aria) to tell various messages and so on...
We need to track user's progress, because it is multiplayer game, so we picked mysql as our database, it's widely used even today. So we created tables for user acount, for towns, messages, alliances, attack_progress, warriours, buildings and began to put things together...
Since we wern't fammiliour with anything but php, we picked that as our main programming tool and connected to the database that way. So we could store the progress player has and even all the progress could be sent to the offline player via it's email address in order to reach user when the danger is coming. Since PHP is almost on every online web host service even today, you can definitely pick it up and work with it. Please realise that I don't say that it is the best or even a wise choice, it's just one of many ways to achieve the result and python or some other languages can help you do just that. Anyway, when you start to build a building, you put the record to the table and reference it to the user by it's unique ID and that way we can use front-end to show user the building progress, how many seconds left untill it's done, what benefit he/she will get after it's complete...
As a programming paradigm, you totally should pick object-orriented style. I remember we didn't know that stuff yet so we wrote everything procedural way and believe me, that's not a good choice and when I really think about it, I don't understand how we did that game at all PHP isn't that good as Python or some C languages in object-orriented style, but it does have the most important features either so there is no reason to run from that if you decide to pick it up. Since I write PHP professionally these days, so I know what I'm talking about here.
These technologies are totally fine if you will create game like this, however...
Lets pick another type of game in order to get most of it:
Imagine you will create a card game. I know that we talk about RPG's here, but logic and interaction is the same so why not to choose what I like more that RPG to describe things you will face. If for instance you will make a game like UNO, where few players can sit around the table and play together. They do interact and you need to know when (in almost real-time) other put the card on the battle field / arena. In a game like this, you need more things to deal with:
Perhaps you will pick web sockets, which is still considered as a new technology so implementation on the server side might be harder than usual. Another way is to use ajax and json to transfer information between server and client (your web browser is considered client here), so ajax can make XMLHTTPRequest and send an information via post or get (via url) to the server and request the information back from it (encoded in json for example), which javascript can decode to the object straight away. This way you can pool information from server each 3 seconds (or more freequently) to check if state of the game is changed and if it did, you just parse that json to update user with the newest information on the gaming board. You can keep your cards in database and link everything with foreign keys, thats is all for you to start
Don't forget that in web is harder to protect from various cheeting methods, because js on the client side is accessible to the person for an injection, but for a simple game it isn't so important as it seems.