You cannot. Just IANA can.
Control over most top-level domain names is assigned to responsible organizations through the Internet Corporation for Designated Names and Amounts (ICANN), which works the web Designated Amounts Authority (IANA) and manages maintaining the DNS root zone.
Here's a listing of accessible TLDs:
You are able to run your personal nameserver and give a new tld there. But this will not assist you to much, because the TLD are only visible towards the customers who're making use of your own nameserver. The "official" TLD like ".ly" are nations, see: official list