There are a number of possible causes for heel pain but a common and very painful one
is Planter Fasciitis. The most indicative symptom is pain under the foot when first getting out of bed in the morning, subsiding gradually with walking. In some advanced cases it is painful all day but usually patients with this condition remember a stage where it was only in the morning.
There are a number of treatments offered for this including cortico-steroid injections under the heel, stretching exercises, special insoles to put in your shoes and in extreme cases surgery is sometimes offered.
Which works for you would depend on the severity of the case but a good starting point for most patients is orthotic insoles that change the way your feet move when you walk and take pressure off the effected area. These are prescription only insoles and shouldn't be confused with those you can buy over the counter in a pharmacy. The good news is they needn't be expensive. In most cases pre-made prescription insoles can be sufficient along with stretching exercises with the much more expensive custom made insoles reserved for very persistent cases.