There are any number of care plan books out there. Go to the bookstore (online or hard-copy) or the library and look over a few if your faculty hasn't assigned you one or hasn't given you a template they want you to follow. Ask them, too.
The basic elements are:
Subjective: What does the patient tell you about what's happening?
Objective: What are your observations/chart findings/measurements that relate to the possible problem?
Assessment: What do you think is going on and why? (That's your nursing diagnosis with rationales)
Plan: What are your nursing interventions going to be, and how will you reassess how they work?
Another way to look at this is ADPIE: Assessment, Diagnosis, Plan, Intervention, Evaluation, which would include all of the above