point, mark, speck, decimal pt
點 centers on a small, precise mark or dot: a point, a speck, or a decimal point. The idea extends naturally to marking or indicating something with a small touch.
點 combines 黑 (black) with 占, which likely contributes the sound and the idea of a small mark or dot, as in a black speck or point.
The left side 黑 suggests black ink, and the right side 占 looks like a small mark or dot being placed. Imagine dipping a pen in black ink and making a tiny point on paper.
For テン, picture making ten tiny dots with black ink: ten -> テン, and each dot is a perfect point.