If you want to work from your computer at home, you are probably going to have to do it as a business owner, rather than as an employee. There are no online work-at-home "jobs".
When you apply for a job offline, in the bricks and mortar world, do you have to pay anything? Of course not. It should be the same in the online world. If you are asked to pay any money, at best, it is a business opportunity, but more likely it is just a scam.
Be very careful that you don't get scammed.
I do affiliate marketing online. I've been doing it for a year and I'm getting ready to quit my regular job, as I am now making over $10k per month. However, it takes dedicated, persistent work, at least a few thousand of initial working capital, decent organizational skills, and a healthy dose of motivation, but you can make a living at it if you stick with it.
But that is a business.
Starting a business requires a lot of work and dedication. You cannot start a business this week and expect to be earning a good profit next week.
Employees tend to have a "job" mindset whereby they worked this week, so they expect to see results this week (i.e. a paycheck this week).
In business, you don't see results like that. Take, for instance, starting a new restaurant. You'll first have to choose a location. The most successful restaurants have their own location, with their own parking lots.
If you wanted to open a restaurant like that, you'd spend a couple of months looking for the right location. Then you'd spend thousands of dollars for an architect to help design the plans with you. Then you'd spend thousands of dollars getting your plans approved by the local authorities.
And then, after all that, you'd be approved to spend hundreds of thousands of dollars on hiring a firm to actually build your building. And after that, you'd spend tens of thousands of dollars to install the interior decorations.
And then you'd spend thousands of dollars hiring employees and training them, as well as having them prepare for the grand opening.
And then, after over a year and spending over a half million dollars, you'd be ready to open the doors and start earning your first dollar.
I say this to illustrate my point: businesses take time and money up front to develop. In the longer period of time, this time and money invested up front will pay off.
But businesses take time to develop!
It is not like being an employee where you get instant results, meaning work this week, get paid this week.
Business is not like that.
If you want something easy, with no investment, you could probably make $500 to $1000 per month getting paid by companies to write postings on blogs about their products. That's about the only legitimate way that I know of to earn money online without any investment.
I wish you much business success, if you choose to go that route.