What does it mean to loan money to someone?
To loan money to someone means to give your own money to someone else for a period of time. Then, the receiver will eventually pay the lender back the money (usually with interest).
Basically they mean the same thing. You can give someone a loan, or allow them credit which means to let them borrow money from you. However there is a slightly different use of the term 'credit' in accounting: there it means to increase in value (to reduce in valid is 'debit'). Even more confusing is the term 'creditor' which means 'someone to whom you owe money' (a 'debtor' is 'someone who owes you money).
Loan can be a Noun or a Verb. A loan is an object or amount of money given to someone in trust that it will be returned to them. In this definition, loan is a noun. If I were to use loan as an action (a verb), I would be "loaning someone my car for the afternoon". An adjective is a word that describes a noun. "Loan" cannot describe anything.