I'm using capital letters of the fourth level, bout just the letters. The accents are not working
Let's take an example to explain you:
This is:
a = just press the key
A = shift + a
b = fn + a
B = shift + fn + a
NOTE: you can't type B if you keep shift and fn pressed when you are typing the a key.
You have to lock one of the two keys: so, for example, double press shift and type fn + a. Also locking fn and shift is ok. Locking fn and pressing shift + a is not always working.