Hi there! I am interested in creating a browser-based sim game and am not quite sure where to start. I am completely new to this, apart from some basic knowledge of HTML. 

I have a complete idea of what the site would be and look like and have even drawn up mock pages for everything from the home page, to a player's account page, etc. Coding and creating it is all that is left, I guess? After some Google searching, as I'm understanding it would be wise for me to learn HTML, CSS, and Javascript? What else should I be educating myself on? Is there any software that would be useful to me?

Any help and advice would be wonderful! Thank you!

I've actually used game maker studio in its early phases, and it really that bad. being that you're a beginner, this might just  be the piece of software you need to help make the learning process a bit easier on you. I too would recommend giving it a try.

Learn the basics of a web design - css, html, js    you can use w3schools, codeacademy  whatever works

You can try writing your first prototype for months and release it on kongregate to see the feedback while you are learning more stuff.

I chose to learn vanilla javascript before moving to frameworks and all that neat stuff

Thank you for the replies!

The game I had in mind will involve sim animals. If I wanted to add in some sort of artificial genetics system, would that involve Javascript or something else?

I am currently learning through FreeCodeCamp, but will check out your other suggestions as well! I know this is quite ambitious for someone who is totally new to this, but I am very willing to learn and put in the work.

You could do it two ways, well it all depends on how heavy the game you want to make. As it is your early stage of learning development, you might want to do the simpler method.

The simple one and the short one is you can write the logic in javascript, that's fine. You can simulate a lot of complicated systems in plain javascript.

For the serious project you would want to use serverside compiling and pull up the requests with ajax/json, so it wouldn't take calculation time from your website, you would just send the arguments to the server and do the computing of your genetic system or whatever there and send the result off to the front-end. That also adds the security layer to your project, but that's for later i suppose. 

It's more important that you play with what you've got now and then expand on your knowledge as you fill the gaps.

By the way, when you decide to move to frameworks some technical stuff is much easier to handle