Turn my white light off - I'm incomprehensible

You can see where I am, but you can't see me.
Creating me by hand you let the hand free.

Creating me by tools you use the largest one.
I make my cousins be more clear to everyone.

The shortest valid answer would be invisible.
Turn my white light off - I'm incomprehensible.

Who/What am I?

You are

whitespace.

You can see where I am, but you can't see me.

You can't see whitespace itself as it's the absence of pixels/ink/etc., but you can see the unfilled gap it occupies.

Creating me by hand you let the hand free.

To create whitespace by hand you, well, just don't draw or write in it.

Creating me by tools you use the largest one.

Space bar is most often used for adding whitespace. Other keys that also create whitespace - TAB and Enter - are also larger than other keys that actually create characters on their own (SHIFT/CapsLock are bigger but they are modifiers, not character inputs in their own right).

I make my cousins be more clear to everyone.

Whitespace between non-whitespace characters (the cousins) makes the text far more clear than it would be without whitespace.

The shortest valid answer would be invisible.

The shortest whitespace is a CR, which cannot be seen at all as it leaves no actual space behind.

Turn my white light off - I'm incomprehensible.

whitespace is something altogether different.

• Perfect explanation of all the lines. Congratulations. Jan 17, 2017 at 7:14
• Humph. You stole my answer :P Jan 17, 2017 at 13:27
• @Mithrandir WHAT? I came up with that entirely on my own, I can't believe you would accuse me of such shenanigans, this is an outrage! I am so offended! I am going to DO SOMETHING ABOUT THIS! I've never been so insulted in all my life! I'm going to write to the Meta community, the Mods, the site administrator, and my Congressman to protes .... nah, you're right, I totally stole your answer. :) (I fixed it tho!)
– Rubio
Jan 17, 2017 at 16:43
• I don't understand the last line (and title). What's incomprehensible about "space" or space? The word "space" can even still mean the same as "whitespace". Jan 19, 2017 at 19:29

A space

You can see where I am, but you can't see me.

There's a space there

Creating me by hand you let the hand free.

Not sure

Creating me by tools you use the largest one.

Largest key on the keyboard

I make my cousins be more clear to everyone.