At the top left, the number 42 is called the atomic number. This is what identifies the element (every element has a different number...)
The atomic mass is found at the bottom... This would be the number 95.94 - rounded - 96 (this is the most common isotope - don't worry about the vocabulary rn - you might not have learnt this yet :) )
The number of valence electrons is the number of electrons in the atom's outermost orbit... The maximum number of valence electrons an element can have is 8... So, in this case, there is 1 valence electron.
The number of electrons in the n = 3 shell is identified at the top right... It is the third number in the column (18)
The number of neutrons is found by subtracting the atomic number (the number at the top left) by the atomic mass (number at the bottom).
So, 96 - 42 = 54