The white keys
Look at the black keys: they come in groups of two and three, and that pattern repeats along the whole piano. The black keys are your map — every white key can be found by looking at them.
C is the white key just LEFT of every group of TWO black keys. From C, the white keys go up the alphabet: C, D, E, F, G, A, B — and then the pattern starts again at the next C.
Two more anchors help: F sits just left of every group of THREE black keys, and the distance from one C to the next is called an octave.
C D E F G A B — then it repeats
C
D
E
F
G
A
B
C
The white keys of one octave. Note C left of the two black keys.
Practise this in the trainer — it opens with this lesson the first time the concept comes up.