The Double Bass is the first transposing instrument encountered in a traditional orchestration class. Printed notes sound an octave lower. The double bass can play incredibly low - near the bottom of our hearing range.
Although E is listed as the bottom range, some basses have a C extension that allows them to descend down to the C, instead of an E string. However, since not all basses have this, writing this low is not recommended for church music.
Due to its deep timbre, the double bass is not used every time the rest of the strings are used - especially in lighter passages. Often the double bass doubles the cello (but sounding down an octave).
The upright bass is used especially in jazz, notably for the "walking bass" (scalar patterns based off the blues scale). Pizzicato is notably louder than with the other strings.
Of all the instruments, the double bass is the least-agile of the strings. Rapid passages within an ensemble are not recommended though classical composers have used it to great effect (Mahler 2nd Symphony).
In an church orchestral setting, the double bass and tuba often double each other, although several other instruments can also play in some of the lowest range, such as the bari sax, bassoon, and bass trombone.