I'm afraid you won't learn programming with a tutorial...

Anyway:

http://www.cplusplus.com/doc/tutorial/

That's some place to start

If you guys are interested in Python.. I found PyQt4 very easy to pick up and use. Install the python2.5-qt4 files and the -dev files and get to coding.

I found:
http://zetcode.com/tutorials/pyqt4/firstprograms/
and
http://zetcode.com/tutorials/pyqt4/dialogs/

To have excellent example programs to get started. Also, when using QT, QT Designer is the best way to design your UI. Just save the file.ui somewhere and run:
Then you include it in your code (a separate .py file):
Another one that shows the relation between pyuic4 and qt designer step by step:

http://www.rkblog.rk.edu.pl/w/p/introduction-pyqt4/

ETA: It should be warned the one bad thing about PyQt4 right now is that the python2.5-qt4 libraries are not optified. They eat up a lot of root space, and make apps less desirable to users. Plus, your app will be stuck in extras-devel until they (python-qt bindings) also make it to extras-testing/extras (because they are dependencies.)

C++ builds on C. and from what i understand, little C++ code actually makes use of what it adds to C.

i can't speak for python, but C++ will probably jump start your programming career, since an object-oriented programming language will facilitate learning java, vb.net, c#, etc.

Thanks. I'm 15 and i'd really like to write apps for N900. Just didn't know from where to start. Now i'm gonna start learning C++.

Your age is irrelevant unless you are renting a car. I'm 40+ years older than you, yet don't doubt that you could teach me a thing or six.

You don't mention if you have another Linux machine available to you. Get one. You'll have an easier time learning about the underlying operating system from a desktop than from the N900, and you'll eventually have to suffer the SDK anyway. Debian is your first choice (Maemo is built on Debian after all) and Ubuntu is your second choice (also built on Debian and n00bie friendly).

People here keep saying "Python". That's a useful skill, and you'll get results from it quicker. Distributing Python apps on N900 is problematic, but for your own device it'll work just fine.

C++ is a can of worms, and you can easily get lost in the forest. I wouldn't recommend it for anybody's first programming language. (That said, if you become a serious developer on the platform there is no way you'll be able to avoid it.) Just be aware that C++ has a high activation energy. When you start dabbling in C++, you'll be obligated to drop back to your Debian desktop because that's where the SDK is. You'll have to learn about the GNU toolchain, a nontrivial undertaking by itself.

So my recommendation is: install Debian, learn to drive around the Linux filesystem, write a handful of Python toy applications, install Python on your N900, run your toy applications on it, then start playing with PyQt. That'll give you a solid background when you graduate to C++, the SDK, the toolchain, and the Debian package system.

Once the Python-qt bindings are optified I don't see a huge benefit in using C++. It's more native, but I think Python would take less maintenance effort: especially when the next device hits.

Not saying I think C++ is bad.. I'll likely use it at some point as well. But python is quite snappy, the overhead at being interpreted doesn't seem to be a big issue. And, just one executable for armel/i386. That's always nice .

With madde, the development is far easier than before (in C++)
no need for the SDK anymore

You said that you want to make an app, but what type ? a game ? an application using a lot of UI elements ? a widget for the desktop ?

My advice would be to get your head wrapped around the object-oriented paradigm, which is what QT and C++ is focused on. It's more the software design paradigm than the language itself that's a hurdle. When it comes down to it, C, C++, python, and java aren't all that different. What i mean by that is you can shoehorn any of them into producing really poorly designed software.

What's really different is the design paradigm, and that's not something you learn fooling around with a language reference. However, that's mostly with a longer term, future-proof perspective...

If you just want a quick-and-dirty start on writing apps for N900, not a longer-term, but more universally useful approach, go through the "hello world" tutorial for python and then grab one of the smaller python apps from the repository and take it apart and modify it and see what happens. Never underestimate the value of learning by example when it comes to development.

I'm not sure what its like today, but I remember seeing employment ads where companies were paying people $130K +, to "learn" C++.