What is to lend?
Prestar- to lend Prestame- lend me
2 Answers
To borrow = pedir prestado
To lend = prestar
Sometimes dejar is also used to mean 'lend':
lend me your pen, déjame tu boli
Kiwi's answer is very good as far as it goes but I would also add that the context in which you intend to use your words/phrase is critical!.
In what context are you intending to use these phrases that Kiwi gave you?
I know that in English you can transfer short phrases to use in different contexts eg: Would you please lend it to me? or I wouldn't do that if I were you!
We can get away with that in English because we often have/use one main verb which can be used in a variety of ways eg to get, which can be really confusing to people learning the language because it can mean so many different things in various contexts; to obtain, to receive, to buy, etc...and that is apart from phrasal verbs such as you'll' get there (You'll succeed).
However, when learning to translate into Spanish and probably all other world languages it is important to consider the context, that is the way in which we are intending to use the words/phrase and to appreciate that we are likely to need to use a different construction for different contexts! Look carefully in any good, bi-lingual (eg English , Spanish) dictionary and you can hardly fail to notice that different options are offered which vary according to the way you want to use them!
I will finish by giving you some examples* based on your question
Borrow: May I borrow your pencil for a moment? = ¿Me prestas o me dejas su lápiz un momento?
To borrow something from somebody: pedirle prestado algo a alguien
Le pedí una escalera prestada a Tim = I borrowed a ladder from Tim.
To borrow a book from the library: (sacar)
I borrowed it from the library: = Lo saqué de la biblioteca
To borrow something from something
An idea I borrowed from television = Una idea que saqué de la televisión .
To lend: prestar, dejar
ex's: The library also lends records (Or CDS) = La biblioteca también presta discos (CDs) o deja discos en préstamo.
As you can see, there is no one way to say something in Spanish as there sometimes is in English it will depend to a great extent on the context, so please, in future, give examples of how you are intending to use your sentence/s. This will enable people answering to give you more accurate answers tailored to your specific needs!
Thank you and I hope this helps you 
All examples* given courtesy of Oxford Spanish Dictionary 3rd edition
Disclaimer: Notice to native Spanish speakers: Great care has been taken to accurately copy examples from the Oxford Spanish dictionary but If there are mistakes please let me know and I will double check the exmples given but if I have copied them correctly I am not responsible for the accuracy of the Spanish given in this or any other dictionary.
