Sequence alignment looks for overlapping element chains in two or more protein strands. The more overlaps there are, the more likely it is that the strands have some sort of relationship. This is helpful for determining evolutionary relationships between organisms.
Sequence alignment also serves an important role in developing new drugs and vaccines. By identifying the strand of a virus, scientists are better able to develop medicine to fight it.
A pairwise alignment compares the overlapping chains of elements in two protein strands. The strands are written out with one on top of the other, and common chains are identified.
A multiple sequence alignment is similar to a pairwise sequence alignment, but it is done with more than two strands. The amount of overlapping elemental chains is smaller because there are more strands. A multiple sequence alignment can sometimes appear in a tree-shape form.
Unlike a pairwise alignment or a sequence alignment, a structural alignment examines the entirety of two or more protein strands and does not look at individual elemental chains. Structural alignments cannot be written out, but instead must be examined three-dimensionally.