"Lend" is a verb. In proper English, "loan" is a noun, although nowadays, many native speakers are using it as a verb as well. The difference is that they are different parts of speech, but the meaning is the same.

Yes, "to lend something" and "to loan something" are virtually interchangeable. Typically, if someone is given money temporarily from a bank, it would be called "a loan." Such in: "I was given a large loan from the bank." But you could also say: "I need the bank to lend me some money."

Here is a detailed explanation: http://www.quickanddirtytips.com/education/grammar/loan-versus-lend