If you know the home you want to make an offer on then you can contact that agent directly or call the office and request an agent to represent you. Before you make the offer, make sure that you are financially able to purchase that home because a seller is going to request confirmation with an approval letter.
The realtor that you work with can go through the details with you on home purchasing. But ask all of the questions that come to you - no question is a dumb question. Also, ask them "is there anything I didn't ask that I should. Bottom line understand what you are getting into. Best of luck.