101 Languages and Language Helpers (see Resources below) offer very helpful pages to get an idea of the basics of the Latvian language.
101 Languages can be used as a small phrasebook; the site offers thematic vocabulary as well as phonetic transcriptions for foreign learners. Language Helpers offers a somewhat larger vocabulary selection as well as audio recordings of every item; audio tools are important when learning Latvian to learn to hear the differences between long and short vowels as well as a few unfamiliar sounds.
The University of Washington hosts an online version of the "Basic Latvian" textbook written by Joseph Lelis. In addition to providing in-depth history and grammar information for the language, there are also audio resources to accompany dialogues in colloquial Latvian based on everyday situations.
My Language Exchange (see Resources below) is an online service that pairs people who speak different native languages so that they can share their own language knowledge with each other. While your partner helps you with your Latvian, you can help him with his English.
To investigate an unfamiliar word or phrase or simply to expand your Latvian vocabulary, use Promt's online translation service. The equivalent of one large paragraph of text can be translated at once and the service is bi-directional (Latvian-English-Latvian).