How is this different from other password generators?

It never leaves your browser, and the randomness comes from crypto.getRandomValues rather than Math.random.

What does the entropy number mean?

It is how many bits of genuine randomness the password carries, worked out from its length and the size of the character set.

Should I turn off symbols?

Only if something refuses to accept them.

Generate a strong password

Real randomness, generated on your machine and never transmitted.

Pick at least one character type

128 bits of entropy. Overkill, in a good way.

Generated in your browser using crypto.getRandomValues, with rejection sampling so no character is likelier than another. It is never sent anywhere, which is the only way a generated password can be trusted.

Questions

How is this different from other password generators?: It never leaves your browser, and the randomness comes from crypto.getRandomValues rather than Math.random.
What does the entropy number mean?: It is how many bits of genuine randomness the password carries, worked out from its length and the size of the character set.
Should I turn off symbols?: Only if something refuses to accept them.