Trees that drop their leaves each autumn are called 'deciduous', from the Latin for 'to fall'. Alternative names for deciduous trees are broadleaves or hardwoods. Some of the more common species are oak, poplar, beech, apple and chestnut.
Coniferous trees have small, waxy and usually narrow leaves (needles or flat scales). 'Coniferous' means that it is a cone-bearing tree. The most common conifers are spruces, pines and firs. Alternative names used for coniferous trees are evergreens, softwoods and (appropriately enough) conifers. However, the name evergreen is not really a good synonym. Laurel, acacia and eucalyptus are also evergreens, and although not deciduous, they are not cone-bearing trees (they also definitely have leaves rather than needles).
Deciduous and coniferous sound like two distinct types of tree, and generally they are, but there are a few oddities. The larch is a deciduous conifer: it drops its needles every year in the autumn.
Possibly the most simple answer is that deciduous trees lose their leaves at approximately the same time each year (autumn) and grow them back in the spring. Coniferous trees do shed their leaves (their needles) they are never completely bare, and the needles remain intact and functioning throughout the year.
Maple, oak and elm are examples of deciduous trees.
Conifers such as pine and spruce are examples of coniferous trees.
Deciduous trees typically lose their leaves at some point during their season, during either very cold or a very dry season. These are typically hardwood trees also known as broadleaf trees. Conifers are typically needle leaf trees also known as softwood trees. However one conifer tree known as tamarack is known to be deciduous since it loses its needles during the winter.
Deciduous trees have leaves that fall of the tree in the winter time due to the fact that they have carotenoids and Coniferous trees have small waxy leaves that don't fall off due to the fact that they don't have carotenoids.
Coniferous trees don't lose their leaves/needles all at once and stay green during the winter. Deciduous trees are more of a flat leaf and lose all their leaves during the fall and are basic sticks in the winter.