Step 1: Do not show discomfort during your conversation.
Step 2: Keep your mind open - your teenager might know things that you were not aware of. You might learn something new.
Step 3: Talk about STDs, but do not be harsh. That might cause your teenager to close up and distance herself from the conversation.
Step 4: Talk to your teenager about safe sex and abstinence. Also consider the possibility that your teenager might already be practicing sex.
Step 5: Let your teenager know that she can talk to you about anything. Be there for her by considering all her issues.