Yes, FUNDAMENTALS is a Scrabble word!

Letter values in Scrabble US: F 4, U 1, N 1, D 2, A 1, M 3, E 1, N 1, T 1, A 1, L 1, S 1.

Is it a valid word?

FUNDAMENTALS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

principles from which other truths can be derived
any factor that could be considered important to the understanding of a particular business
the lowest tone of a harmonic series

Also: fundamental principle, basic principle, fundamental frequency, first harmonic.