You can plant it and might bloom again in the summer. They naturally bloom in June or July. If you take care of it, it will likely bloom again next summer in June or July.

Here are the instructions:

http://plantanswers.tamu.edu/publications/lily/lily.html the planting instructions are about 5 paragraphs from the bottom.

You can continue to grow your Easter Lily after it has finished blooming although it is usually very difficult to force Easter lilies into bloom a second time indoors.
Once your lily have finished blooming, place the pot in a sunny location in the home until all danger of frost has passed at which time you can move the pot to a sunny location outdoors (usually, sometime after May 15). Prepare a sunny location in the garden using a well drained commercial planting mix, or a mix of one part soil, one part peat moss and one part perlite. (Good drainage is essential for lilies.) Set the entire pot and plant into the ground until the foliage has died back, then gently remove it from the pot and plant it directly into the ground. Spread the root ball by gently pulling upward and outward from the center to loosen the clumped and matted roots. Plant it a little deeper than what it was growing in the pot (with the bulb about three inches below the soil surface). Lilies should be planted at least 12 to 18 inches apart in a deep enough hole that the bulbs can be placed in it with the roots spread out and down, as they naturally grow. Spread the roots and work the prepared soil in around the bulbs making certain that there are no air pockets around the roots. Water thoroughly after planting