Philosophy of language studies (mainly human) language and is a area of Philosophy closely connected to Logic. It aspires understanding of meaning (semantics) by systematical analysis.
Language is something you learn and something you use.
By using language you can do things ("I declare you ...") or make other people do things ("Pass me the butter!"). You can declare facts ("The earth is flat.") or feelings ("I feel sad.") Language can be understood, misunderstood or not understood at all. Language somehow connects itself to the real world ("Mount Everest"), to abstract concepts ("evil itself"), to things, on which' reality only some people agree ("heaven and hell") and to categories, where we are unsure, whether they are abstract or simply describe one or all of the elements of a defined set - does a swan stand for a concept, for an idea or for the physical reality of all the swans in the world?
We see, that the meaning of language is influenced by many factors, which could be categorized into a) the way language refers to the world, and b) the logic of the sentence. While both aspects are dealt with both in philosophy and in linguistics, the latter of course is subject of logic.
Modern logic is mostly dealing with logic from the perspective of language.