Since Yahoo Answers is not intended as a chat site you have to be careful not to be chatting, see the link below or you could be reported. The best way however, you could click on their avatar, if they accept ims or emails click on the appropriate one and follow the prompts. If the question is still open: click on the "edit" link below your question then "add details" add your note, preview and submit.
If the question is already resolved: You can't answer it, you can only leave a comment (you can leave a comment by clicking on the "comment" button on the action bar)
If the question is still open: You can answer it by clicking "Answer question."
Comments
Since Yahoo Answers is not intended as a chat site you have to be careful not to be chatting, see the link below or you could be reported. The best way however, you could click on their avatar, if they accept ims or emails click on the appropriate one and follow the prompts. If the question is still open: click on the "edit" link below your question then "add details" add your note, preview and submit.
http://help.yahoo.com/l/us/yahoo/answers/abuse/gui...
If the question is already resolved: You can't answer it, you can only leave a comment (you can leave a comment by clicking on the "comment" button on the action bar)
If the question is still open: You can answer it by clicking "Answer question."
pick a category
go to the Open Questions
click on one that you want to answer
read it
click on the blue "answer this question" button
type in your answer
hit 'preview'
re-read your answer
correct as needed
hit 'submit'
Repeat as necessary
;o)