How can I hide the label saying "URL*" from content creation form when using the link module?
Look at the Manage Display tab of your content type. On that page you can set how the label is displayed:


Above
Inline
Hidden


and how your link displays:


Title, as link (default)
Title, as plain text
URL, as link
URL, as plain text
URL, absolute
Domain, as link
Short, as link with title "Link"
Label, as link with label as title
Separate title and URL
Hidden