The majority of groups maintain a FAQ - Frequently Asked Questions. This document or series of documents attempts to answer questions most frequently posted to the group. Common etiquitte (netiquitte) suggests that you read the FAQ before posting to a newsgroup. The FAQ will let you know whether the group is an appropriate forum for your message and in many cases may answer your question directly.
Most FAQs are posted within the group on a monthly or biweekly basis. The newsgroup news.answers also lists the FAQs for all USENET groups. sci.answers maintains FAQs for all groups in the sci heirarchy. Via the WWW FAQs can be viewed from the List of USENET FAQs.
The sci and bionet groups cover branches of science. Where the two overlap (sci.biology vs bionet.xxx), the sci groups generally provide a more basic discussion of the topic while the bionet groups are more oriented towards research. Outside of biology sci.physics and sci.chem disucss topics in physics and chemistry, respectively. Computer topics generally fall under the comp heirarchy of groups. Your browser will need to be plugged into a 'newserver' to access the above two links.
If you don't have access to USENET you can still read certain groups via the WWW.