What to use to create a forum or a social.network?

It depends on your knowledge and capabilities:

You can write, there is nobody will be anything to restrict what functionality you want - so be it. It's all written in visual studio,for example. But the downside is that it is long and difficult (unless you can take the blanks and complete them)

Or you buy\\find the software to create forums\\social. networks.

Personally, I tried this algorithm:
1. Bought a domain on reg.ru (no ads)
2. There's also bought and hosting
3. Hosting set wordpress
4. Profit

Can also see there is a engine for blogs and forums, and social. networks.

But using the engine you will be limited. Wordpress will have to buy, because there are only 3 themes (all the rest like these 3, just color\\pictures of others)

You start to understand who you are:

1) user
2) locksmith
3) engineer

all these types of creators of social networks can make for example a forum or blog in three different ways:

1) use a ready engine of WordPress and under to invent it (you can hire contractors)
2) to learn programming and standard frameworks and assemble your engine the social network (you can hire contractors)
3) to study the craft at the University level, studying for five years, and to become an engineer and to be able to do anything from scratch, all while your code is no clutter and fast