Creating membership websites is one option for making money online, but you really need to know what you are doing and figure out if you really want to do it. A membership website is creating a site that charges money for accessing specific information or for taking an online course. It is usually a yearly fee or reoccurring monthly fee. Yes it is about $$$.$$. With a membership site you really need to have something of high value to offer to people though to make them want to be a member or continue to be a member.
It also is really high maintenance because you will need to offer outstanding support and customer service and answer people's questions. You will also have to be adding new information each month or so. It really can be too much work.
The same information can often be provided in a book or ebook or even in a magazine format.
If you have gotten over the 'it's too hard' and 'it requires too much time and energy' problem and still want to create a membership website, I recommend using WordPress and the Wishlist Member Plugin. The software itself will have a big learning curve. Wishlist was the easiest I could find.
I have used it for my site www.massagepracticebuilder.com but recently used it for an actual association membership for a non-profit organization.
Before you start a membership site though, you will really need to have a website/blog set up and have a mailing list that you can promote your membership program to. You can start with having all of the information for free as you build and then start charging to access your value content. You use the free content to build trust with your readers so they will readily pay for access to more of your content.
It really needs to be unique content that you can't find for free online or if it is a big topic like creating an online business where most of the info is online, you can be a content coagulator and put it all together for people in a very unique way.
I have found the time and hassles of running and managing a membership program are just too much for me. I much prefer just writing ebooks/books and selling the information.
You can also just have the content be for free and make money in some of the other ways such as using Google Adsense and/or affiliate programs to make money.