How do you use a double bass?

Answer 1

The standard tuning for double bass is in fourths with the highest string tuned to G two octaves below middle C (actually an octave and a fourth below middle C to be precise which would be the bottom line on the Bass (or F) clef.

The remaining strings of course would be D, A, and E below this G string.

It is common for orchestral players to extend the length of the low E string with a fingerboard extension to extend down to a C.

In addition, it is not uncommon to find find string basses in orchestra especially in Germany and Austria.

In this case the lowest string is tuned to a B below the low E string or sometimes to the C below.

Answer 2

This depends, the 5 string has the standard four strings (EADG) but the fifth makes everything complicated.

If your bass has the five strings in the order of B E A D G then you get the B in tune using another guitar or a tuner or some reliable tone (or if you're particularly skilled you can tune a B by ear) then the other strings should sound identical to the fifth fret on the string before them. i.e you pluck the fifth fret on the B string and this is your E, then the fifth fret on the E string, this is your A.

If your bass has the strings in the order of E A D G B then you tune the E and again the fifth fret of each gives you the next strings open note, EXCEPT when you reach the G string, its the fourth fret that gives you the B