How do hip flexor strains affect my body?
A hip flexor strain is a muscle problem, so the way it shows up depends on what the muscle just went through. Here is the basic picture.
Muscle fibers stretched past their limit
Cleveland Clinic says that when you overuse a muscle, the strands of muscle fiber are stretched beyond their limit and tear apart.

Reading about nearby strains
The Cleveland Clinic page on groin strain lists symptoms, causes and tests for a nearby muscle group. The Cleveland Clinic overview of muscle strains covers strains in general.
Tracking symptoms and booking a visit
For a short, free explanation of strains versus sprains, read the MedlinePlus page on strains and sprains. Then watch how your own symptoms change over a few days and write them down.
If you live near Woodland Park and the problem is not improving, book a visit to have it examined.
Noting what you were doing
Pay attention to what you were doing when the problem started. That detail helps any clinician who sees you.