If you have a passion for programming you are halfway there already.
I started programming in BASIC back in 1980. I thought I would be hopeless at it because I had difficult with mathematics at school. The thing is, programming is much more about logic, Also, at least back in the days before Graphical User Interfaces, the ability to retain arcane coding language terms in your memory without having to look them up all the time.
phpBB is a web based software suite, not a computer language.The phpBB system is coded in PHP. PHP " is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML."
You will learn a lot about how web systems work by setting up and administering a phpBB installation, but unless you start customising the scripts (not recommended at your stage!), you won't necessarily learn much about programming.
These days people seem to want to leap straight in to web development. That's fine, but perhaps also consider installing a commonly used programming language Integrated Development Environment and creating some purely local applications first. The Fundamentals Of Programming you learn from that are transferable skills which you can build on when you take to web development and possibly avoid a lot of frustration. There are Massive Open Online Courses available:
https://www.coursera.org/courses?query= ... ndamentals
Note the abundance of different languages to choose from so go for a generic course first.
The classic teaching language in universities used to be Pascal, but these days students go straight in to 4th Generation Languages and Object Orientated programming.
Over the years, the language I found most difficult to get my (admittedly rather old) head round was Java - particular in the Android phone flavour.
Apart from the specifically web development targeted scripting languages, C is very popular these days.
You could do worse than install a local C# IDE. Microsoft usually allow free installation for non-commercial and student use of Visual Studio:
Sites like Stack Overflow are a useful resource when you get stuck.
Get stuck in and write your first "Hello World!" program. You will need a local machine or a shared web hosting account with PHP (that's all of them) if you want to go straight for what drives phpBB.