Put it in a pot about 2 inches bigger than the bulb is around. WELL draining potting mix. Sink the bulb half way in and water well. I add extra perlite to potting mixes, about equal parts of each. Acclimate it to full Sun and feed regularly.

Why do garden centers put the bulbs in vases with just water when they're trying to sell them in bloom?

There is an Amaryllis Forum which may be helpful. See link below.

Here is a link that might be useful: Amaryllis Hippeastrum Forum