Orchestras tune up to the concert master, usually one of the violinists. So everyone gets to tune one of their strings to the pitch of the one string of the concert master. Almost all of the strings in an orchestra (excepting things like guitar, banjo, lute, sitar) have 4 strings (violin family), with the frequency intervals (ratio of frequencies) between adjacent strings being usually a perfect fifth, or perfect fourth (e.g. string bases) which is the inverse ratio to that of a perfect fifth.
So if I have a violin in my mitt, and I tune my A string to an A from the lead violinist, to put my instrument into tune, I must get the E string to be a perfect fifth above the A, the D string to be a perfect fifth below the A, and the G string to be a perfect fifth below the D. The perfect fifth relationship has the higher string vibrating three times for each two times the lower string vibrates, plus a tiny adjustment to get the frequency ratios of the twelve half-steps in an octave all equal. The adjustment is very small (about 0.11%), you could tune a violin with the fifths all exactly 3 to 2 so that, e.g., the google tuner could still show all four strings as in tune. And the 3 to 2 ratio is about the easiest interval less than an octave to do by ear. So most violinists, cellists, etc with good ears do fine without tuners.
The guitar has an interval of a major third between the G and B strings. The integer ratio of frequencies for this interval is usually given as 5 / 4, but the adjustment to even out the steps in the octave is larger, about 0.79%, and you cannot tune the other notes on a guitar at showtime by moving the frets around, so tuning the guitar (and other fretted instruments) is more like tuning a piano than tuning a violin or cello.