Abarim Publications' online Biblical Hebrew Dictionary
ל
The particle ל (le) is a preposition governing a relationship or a motion towards or into whatever it's placed in front of. It may be translated with to, towards, in order to, in or into, resulting in, for, for the purpose of, with the aim of, with reference to or even belonging to, on behalf of, in view of, etcetera.
It's used is much the same way as the particle על ('al), and they are probably as related to each other as the prefix כ (ke) is to the particle כי (ki), or the particle אשר ('asher) and the prefix ש (shi).