Why do さ and ざ look the same except for the little strokes on the side?


I am learning hiragana and I am looking at sa, shi, su, se, so, and za, ji,
zu, ze, zo. The characters look the same except the "z" characters have little
strokes on the side of the character. Why is this? And what is the difference?
When do we use it, and how?

Example:

さ vs ざ




The reason for the similarity is that they are thought of as being _variants
of the same letter_. The little dots are called 濁点｛だくてん｝, and they designate
that you should say the same sound but voiced instead of unvoiced.

The sounds S, T, and K are always spoken with a burst of air, while the voice
box is silent. When these sounds are "voiced," that is if your voice is making
a noise at the same time as you speak these sounds, they become Z, D, and G
instead. Rather than make entirely new kana columns for the voiced variants of
these sounds, the 濁点 are used.

The one column where the rule might seem a little strange to English ears is
the は・ば・ぱ group. In this case, I would consider ぱ to be unvoiced, ば to be the
voiced version, and は to be a different consonant altogether. This one you
just need to memorize.

