Difference between authorized capital and paid up capital?

Authorized capital is the maximum amount a company is allowed to collect from public by issuing shares. Paid up capital is the amount of capital which a company has currently issued to the public in the form of shares or the public has provided the money to a company for working.

For example:

Authorized capital $1000

Paid Up capital $100

Now a company can issue shares of $900 to the public offering and not more than that.