Lexis (words + their origins) + semantics (meaning of words, both on their own + in relation to other words in the text)
Grammar (building blocks of sentences, e.g. words, phrases, clauses, e.t.c.): Includes syntax (order of the elements in a clause or sentence, e.g. subject, verb, object, e.t.c.)
Discourse: describes the structure of any text (or segment of a text) that is longer than a single sentence. Looking at the way that whole spoken + written texts are structured.
Pragmatics: what we really mean by what we say or write in a given context.
Phonology: the study of the sound system in the language + the effects of its particular features (i.e. looking at consonants, vowels, rhythms, stresses, pace)