I have a question about making a website

For example, similar to a forum,
But user can post pictures

How much does something like this cost?
And where can i find more info about this?

You can make that for free using one of open source projects like discourse, phpbb, or you can host your own Mastodon instance (its like twitter)

Cost depends on hosting, more users = more GBs and traffic = more cost. If you're starting its likely cents per month on something like AWS

Thank you for answering

d2jsp is highly modified Invision Power Board

it will cost about $5/mo for the web server and the domain is usually around $15/year