Imagine a huge game, Skyrim, lets say. Are you going to model the whole world, all the items, characters in the world? No, you've got to pay a bunch of other people to do it. Are you going to write all the diaglog? Are you going to rite all the code that handles all the characters? Design every quest? etc. Skyrim is a multi-million dollar game BTW.

Even for smaller titles, few people can design, code, and draw everything themselves. Typically, they have to hire others to draw and animate everything for them. that's the typical "budget" for many games.

In addition to what BeerNutts said, there's also sound effects and music to consider. While free resources to exist, you can't always find what you need out there. In which case you'll either have to create your own, license royalty free stock effects/music, or pay someone to create it for you. For a one-man indie shop, depending on the scope and quality of the game, outsourcing graphics and audio content creation can realistically cost anywhere from the low hundreds of dollars to tens of thousands.

Why Do you need to fund money to make a game because I'm making a game and I'm confused about it

You don't need anybody else's money if you aren't going to hire anyone and you aren't going to spend money marketing and publishing your game.

So how much money would a 2d side scrolling game cost to publish

No one can tell you that.

It may be 0. It may be 50,000,000. It's up to you.

You have to pay for:

Equipment
Office lease
Employee Salaries / Wages
Software Licenses
Royalties
etc...
etc...

As far as publishing. That has different meanings, and different costs depending on what route you go, and what platforms you choose.

Why Do you need to fund money to make a game because I'm making a game and I'm confused about it

Games are labor intensive and skilled developers/artists don't tend to work for free.

So how much money would a 2d side scrolling game cost to publish

Publishing a game doesn't necessarily cost anything, (services such as steam, Google Play, or Apples Appstore will sell your game for you if it is good enough) (They'll take a portion of the sale price though) and you can always sell it from your own website using for example paypal.

Making a game can cost anything from $0 (assuming you allready have a computer and are using free software) to several millions (There really is no upper limit).
The main cost during development is:
* salaries, skilled developers and artists don't normally work for free.
* software licenses, when people are payed for the time spent its worth spending quite alot of money on software that reduces the amount of time your staff has to spend.

Marketing a game can also cost quite alot of money. (again, no upper limit here really, if you want television ads on all major networks all around the world it will cost alot of money, if you're just gonna use a youtube video and get some of your blogger friends to write about your game you might be able to get away with $0)

So how much money would a 2d side scrolling game cost to publish

It depends. On what platform? Using what monetization method? Are you going to market it, or just fire and forget? Is it a social game?

If you want to make a commercial product (which means it's for profit), odds are you have to invest money into making it attractive to the general consumer. If you're making an indie game, or a very personal project, you don't have to invest even one cent, but you will still have to put a lot of labor into it (hopefully you have a day job or other source of income). I'd say, by the sound of it, you can make your 2D side scroller for free. There are a lot of free game development kits out there. And when it's time to distribute it, post it on your website, hit the forums, put a playthrough on YouTube, etc. I guess it's a matter of intent: make money, or create a game for people to play. Ideally, you want both, but if you're lacking the resources (mainly money), you can still do one of the two. ;)