Website 'Software' to use

I have an idea for a potentially good website. I know HTML, CSS and some PHP. Without going into too much detail I'll try to provide as much info as possible

It will be a website where show off images/plans to make something. I want it so that people can sign up & create a page, upload photo's to the page and create a description/instructions for it. Then they can select categories that their page will apply to and the page is done for people to view and follow it.

Once the page is done people should be able to search using key words and categories to find what they want to help what they are trying to do.

I have the hosting, and the domain name, but I can't find a good website 'software' to use, such as a forum, blog or CMS package. Does anyone know what type of website software would be best to use to achieve this? I don't mind using plugins to add some of the functionality but I am unsure of what software I could use to allow people to sign up, create a page (or multiple if they have different designs or idea's) and then have their website listed on search page or different category list. Can anyone help?