Here's a quick tour of normal language development, with the caveat that even typical children vary widely:
~12 months, first words. (First signs for sign-exposed babies are typically earlier, due to better motor control of the hands.)
~18-24 months, the "naming explosion": acquisition of up to 10 new words a day, using the processes of "fast mapping" (learning the name of a thing after one exposure) and "incidental learning" (learning from the speech of adults who are not talking directly to the child).
~12-24 months, "telegraphic speech": two word constructions, with basic grammatical roles (e.g. adjective-noun, subject-verb, verb-object).
~2-3 years, gradually increasing length of utterances to 3, 4, and 5 words.
~3-5 years increasing mastery of more complex grammatical structures, function words, prefixes and suffixes, etc.
